sailboat black water tank

Yachting Monthly

• Digital edition

What you need to know about a yacht’s black water waste tank

• Toby Heppell
• March 24, 2023

It is now mandatory in most countries to make provision for sewage to be pumped ashore rather than disposed of at sea. So it may be time to install a black water waste holding tank, writes Duncan Kent

Prior to the new millennium, little thought was given to waste disposal from a vessel. Anything you didn’t want on board invariably went straight over the side, including human waste. Thankfully, these days it’s a different matter altogether. Rubbish is widely recycled worldwide, so keeping it on board until going ashore is commonplace, even when ocean sailing. However, black water (sewage) disposal is not such a simple problem to solve, especially on smaller vessels, and it’s of particular concern when you are coastal cruising, anchoring or mooring close to the shore.

Current waste tank regulations

Given the increasing popularity of many northern European, Mediterranean, Pacific and Caribbean anchorages today, I’m convinced no responsible yacht owner would be against banning the direct discharge of black water within at least three miles of the coast. Nothing spoils an early morning dip in crystal clear water more than coming across an unmentionable floating object!

At the time of writing, there are still no mandatory regulations concerning black water disposal at sea from privately owned leisure craft in UK waters, apart from the legal requirement to provide pump-out facilities on inland waterways, but the situation is rapidly changing as other countries update their rules.

Since 2006, the EU Recreational Craft Directive (RCD) has required all new vessels to ‘have provision for a holding tank to be fitted’, although that isn’t the same as actually having a holding tank fitted. Besides, this only applies to new vessels and simply requires a ‘diverter valve’ to be installed into the discharge pipe to enable the waste to be piped into a holding tank.

That said, each country has its own rules about this and some are far stricter than others. For instance, Norway has banned the discharge of sewage within 300m of its coastline, whereas Germany insists you’re 12 nautical miles away before you even think about it. And if you’re even spotted with bubbles emanating from your boat in a Turkish marina you could be fined massively and possibly even imprisoned!

Generally, a holding tank doesn’t necessarily have to be permanently installed (although thankfully most boatbuilders today do).

UK black water regulations currently only apply to inland waters

In theory you could simply divert the waste into a freestanding jerry can or similar for disposal ashore, but this could end up being very unpleasant in rough seas and awkward to empty ashore without considerable mess.

Many boatbuilders that do install them from new, however, often only do so for a single head, leaving others on larger, multi-head yachts to be effectively unusable in prohibited sea areas.

Waste tank system design

The most common setup in new production boats is to have all the waste go directly into the holding tank, which will have a pipe and deck fitting at the top for pumping out shoreside, like most inland waterways craft have. Seagoing vessels, however, will also have a large diameter outlet at the bottom of the tank, complete with a seacock to allow the waste to gravity-drain overboard when outside the local limit.

This isn’t always the easiest to provide if retrofitting a system, though, as hull and deck fittings ideally need to be aligned (for rodding if necessary) and clear of any other fittings. For this reason, some boat owners simply incorporate a diverter valve into the existing outlet hose from the toilet, allowing the waste to either be pumped directly into the sea or alternatively into a remotely positioned holding tank.

Quick switch: send waste overboard or into a tank with a diverter valve

If this tank only has a deck plate, when the tank is full you are compelled to find a pump-out station, rather than simply sail offshore to empty it.

Tank size: The size of the holding tank will usually be a compromise between the ideal capacity and the space available in a convenient locker.

It should be at least 20 litres capacity, but ideally you should allow for around five litres per person/per day for two days. This means a cruiser, regularly used by a couple plus two guests, should work on a minimum capacity of around 40 litres. Too small and you’ll need to empty it too often; too large and it will add considerable extra weight and use up valuable space.

Location: Most choose to utilise an under-bunk stowage bin as the location for a remote tank, although some boats might have enough room inside the heads. Ideally, it should be positioned as close to the toilet as possible in order to keep hose runs short, but not so close as to force tight bends into any of the pipework. Bear in mind that the longer the inlet hose, the more water you will need to pump down it to clear the waste.

Thought must also be given as to the accessibility of any pumps or diverter valves incorporated into the system and the ease with which all areas can be reached for seasonal cleaning or the clearance of the almost inevitable blockage.

A typical holding tank installation

There are numerous companies producing tanks capable of storing black water. These tanks can be manufactured from stainless steel, GRP or plastic, the latter being either flexible or rigid. Steel tanks are excellent in many respects, but sooner or later their welded seams will begin to rust, expedited by the corrosiveness of the waste. GRP is lighter than steel and almost as odour-free, provided the moulding is perfectly executed and there is no trace of porosity. By far the easiest material, especially for smaller craft, is thick-walled plastic.

Retailers sell a bewildering range of plastic tanks, even some multi-purpose tanks supposedly fit for fuel, water or waste. The truth is many aren’t up to the job so care must be taken when selecting one to make sure it’s suitable for black water.

Dometic’s 15 HTS polyethylene holding tank has 6.3mm walls and costs around £600

It is often difficult to spot the difference between a polyethylene (PE) tank (for fuel, fresh and grey water) and a polypropylene (for black water), but the latter is more resistant to corrosion and odour permeation. Wall thickness also needs to be at least 6mm (1/4in), preferably 8mm (3/8in).

A flexible tank can sometimes solve a tight space problem, but in order to avoid the bladder chafing through on a sharp edge, a smooth-sided box must first be built from plywood and GRP. This creates work and limits overall capacity, so in most cases a rigid tank will prove easier to install.

Choosing a standard tank, many of which are available off the shelf in odd shapes and sizes to fit bow and bilge lockers, will save you money over having a custom tank manufactured to your own specifications.

Modern yachts use gravity tanks to discharge waste

Ancillary equipment – Pumps

Whether you decide to go electric or manual, a tank discharge pump must be man enough for the job. It’s no use using 38mm (1½in) pipes, connectors, and hull fittings if the pump only has 25mm (1in) inlet/outlet spigots. Most manufacturers produce a pump specifically designed for the purpose, usually a large-bore, high-capacity diaphragm device that can be operated manually or electrically, with an integral, non-return valve in its outlet.

It’s also possible to buy and fit 12V macerator pumps that grind up the waste while pumping it out. Their advantage is that a slightly smaller diameter outlet hose can often be used, and the chance of a blockage is reduced. They do, however, use more water than a manual pump, thereby filling the holding tank more quickly.

In modern boats, gravity is usually used to discharge the tank overboard. Although to avoid the danger of blockages with this method the tank outlet and skin fitting need to be large, usually 75-100mm (3-4in) in diameter, which is often not a practical option on a small boat.

New gauges can now indicate the exact level of waste in your holding tank

Ancillary equipment – Valves

Diverter valves are widely available from numerous marine plumbing equipment suppliers and are usually designed for bulkhead mounting. For systems that are pumping out with a head higher than 1m, installing a non-return valve into the exit hose will be essential to stop the contents back-feeding. Once again all valves need to be 38mm (1½in) diameter.

Ancillary equipment – Pipework

This is an important part of the installation, not just for safety reasons, but to ensure no nasty odours can pervade the living quarters. All hoses must be of non-permeable, sanitation grade, flexible PVC and the genuine article will normally be marked accordingly. It’s not particularly cheap, but it’s worth every penny.

As with any sea toilet installation, if the bowl or holding tank are below sea level at any time all pipework connected to a skin fitting must contain a swan-neck bend with an anti-syphon valve at the top. These are freely available in most chandlers for a range of hose diameters. All joints must be double-clipped using good quality, stainless-steel hose clips.

A remote pumped waste tank helps if the layout is awkward

Level gauges: Both electrical and mechanical indicators are available for waste tanks, which differ slightly from the usual water tank sensor in that the sensors are encased to prevent solids from fouling the mechanism.

Gauges are available that indicate the exact level of waste in the tank, but for most installations a simple warning light when the tank is nearly full is adequate.

Ventilation and odour prevention

Venting the tank: The typical odours experienced with poorly installed holding tanks are usually caused by anaerobic bacteria forming in an oxygen-starved environment.

The key to preventing these smells emanating from the tank is ventilation. Supplying oxygen to the tank allows the aerobic bacteria, found naturally in human waste, to carry out the job of breaking itself down. Any gases produced in this process will then be dispersed into the outside air via an overboard vent, preferably installed away from the cockpit area.

Installing a holding tank can be tricky on smaller yachts

Commercially produced tanks are usually supplied with pre-formed inlets and outlets. One of these, positioned as high on the tank as possible, should be the ventilation pipe connection. The vent should ideally exit the tank vertically to prevent any solids blocking the pipe and should then continue to deck level or onto a shell-type skin fitting high on the topsides. The pipe run needs to be kept as short as possible and there should be no tight bends or kinks restricting the airflow. An odour-reducing, active carbon filter can also be installed into the vent pipe without restricting the airflow to the tank.

Water treatment

Water treatment devices, such as the Seasmart sanitation reservoir, are available to kill bacteria in the seawater as it is drawn into the toilet.

The device is plumbed into the inlet hose and contains an environmentally friendly sanitation fluid which, as well as combating incoming seawater bacteria and odour, also claims to reduce the build-up of limescale without having a detrimental effect on the natural aerobic bacteria in the tank.

Simple additives are also available that should eliminate odour from holding tanks and also encourage the breakdown of the waste by natural bacteria. But, whichever additive you choose, don’t be tempted to use domestic toilet cleaner or bleach in either the toilet or the waste holding tank.

US national symbol directing boaters to the nearest pump out station

International black water regulations

Although the UK hasn’t, as yet, implemented any regulations regarding black water waste or holding tanks for recreational craft beyond its inland waterways, the situation internationally is now developing fairly rapidly, and unevenly, with some countries taking a much stricter stance than others.

• France – Boats built after 1 January 2008, either French or foreign flagged, must be fitted with a treatment system or retention tank for black water if they want to access French rivers, ports, moorings or anchorages. Users of older vessels not equipped with treatment systems or holding tanks for black water must comply with the rules that prohibit black water discharge in ports and designated anchoring spots, and therefore use shoreside toilets. It’s forbidden to flush black water into canals and rivers.
• Netherlands – It’s prohibited to discharge black water from any pleasure boat in any inland waterway, lake, or territorial waters.
• Denmark – Boats built before 1 January 1980 do not need a holding tank and can discharge sewage two miles from shore. Boats built after 1 January 1980 but before 1 January 2000, less than 10.5m LOA or with a maximum beam of less than 2.8m, do not need to have a holding tank and can discharge sewage two miles from the shore. All boats built after 1 January 2000 must have a holding tank that can be emptied through a deck fitting.
• Finland – The discharge of untreated sewage from recreational craft is prohibited less than 12 miles from shore.
• Sweden – The discharge of black water and sewage into lakes, inland waters and territorial waters less then 12 miles from shore is strictly prohibited, with spot fines applicable.
• Spain – Vessels cannot discharge untreated sewage within 12 miles from shore.
• Greece – While not actually a legal requirement in Greece, regulations make having a holding tank a practical requirement. Caution should also be exerted when disposing of grey water.
• Turkey – The discharge of any kind of waste may be considered illegal.
• Norway – Discharge from toilets or holding tanks closer than 300m from shore is strictly prohibited.
• Belgium – It is prohibited to discharge or dump any solid or liquid materials which may pollute the water both inland and at sea.
• USA – Federal law states that untreated sewage cannot be discharged, from either a toilet or a holding tank, in inland waters or coastal waters less than three miles from shore.

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Marine Holding-Tank Sensors: How do you Know When the Black Water Level is at Red Alert?

External tank gauges take the guesswork out of liquid levels..

Knowing how full your holding tank is can mean more than simply having peace-of-mind. Whether you’re starting out on a Sunday daysail or a two-week inland cruise, one of your checklist items should always be “Check the tanks.” Unless you are far offshore, realizing the holding tank is full as you attempt to pump the head—or when you pick up the telltale odor from the overflow vent—can be a real problem.

Federal law mandates that all boats with permanent toilets have either an on-board treatment system or a holding tank to store wastewater. Many states with inland lakes and coastal areas have designated them as No Discharge Zones (NDZ) and require that the through-hull and Y-valve for direct discharge ports be sealed to prevent any discharge into the water.

From the freshwater supply to fuel and wastewater, knowing the level of all tanks is a must for comfortable and safe sailing. Several tank-monitor manufacturers now refer to three types of tanks: “fresh” for drinkable water, “gray” for drain water from sinks and showers, and “black” for wastewater holding tanks from toilets. State and federal regulations are changing to address these differences, but not all boats are plumbed with multiple tanks hooked to different through-hulls.

Most older and smaller boats do not have level gauges on any tanks. A good captain “just knew” about how full his tanks were or could judge the level by simply thumping the tank with his knuckles. Occasionally, if the tanks had inspection ports, a visual check with a flashlight or inserting a dipstick was sufficient.

Today, there are several options for measuring tank levels, starting with the simple internal float gauge and progressing to sophisticated ultrasonic capacitance or sonar internal probes. There also are various sensors designed to be mounted on the tank’s exterior, and those are our focus here. We’ll address sensors that are mounted internally in a future article.

What We Tested

Packaged kits containing externally mounted tank level sensors with remote reading displays are becoming increasingly popular due to the fact they don’t come into contact with the holding tank contents. Probes located inside the tank are more likely to be fouled, corrode, and need cleaning.

External sensors use basic capacitance sensors or the electronic Mirus detector cells that read liquid levels on the other side of plastic, polyethylene, and fiberglass tanks. External tank readers are for wastewater and fresh “sweet” water tanks, not aluminum or metal fuel tanks for diesel or gasoline. All of those we tested should work on standard tanks up to 3/8-inch thick, and all come with a one-year warranty.

When choosing a tank-level indicator, bear in mind that at least one side of the tank must be accessible for mounting the external sensor devices.

For this evaluation, Practical Sailor tested five external sensors with their mated display: Raritan Tank Monitor (1510012), Scad Profile Tank Monitor, SensaTank Marine 100, Snake River Acu-Gage Smart Mini, and Snake River Acu-Gage Three-Tank.

Raritan Tank Monitor

Raritan’s tank sensor works on 12-volt DC (other voltages are available). While it can display the liquid levels of four tanks, the kit comes with only two capacitance tank sensor modules. The kit also includes 10 feet of aluminum foil, a 3-amp fuse holder, 12 crimp splice connectors, and a display panel with screws and stick-on labels. These stickers—with universal symbols for “waste,” “gray,” and “fresh”—can be affixed to the display to identify the four buttons. PS testers questioned the durability of these stick-on labels.

The display panel is fairly small, measuring 2.25 inches high by 4.5 inches wide. It has four touch buttons for tank selection, and each has a corresponding hole for calibration. Five LED lights indicate the tank level: empty, quarter-full, half-full, three-quarters full, and full. Testers found these indicator lights to be dim and hard to see in daylight.

Raritan’s instructions are clear and well written—as long as you have a standard size tank. Tanks less than 7.5 inches tall or more than 20 inches tall require adjusting the amount of aluminum foil that is mounted to the side of the tanks.

Calibrating the Raritan is a simple a matter: fill a tank with water up to where you consider it full, then insert a small flat-head screwdriver into the hole above the selected tank’s touchbutton on the display panel, then turn it until all lights are on and then just the full light comes on. Repeat for each tank. The kit includes four small plastic plugs to insert in the holes once calibration is complete.

Before presstime, West Marine marked the Raritan’s Tank Monitor as a “clearance” item, discounting it to $224. Raritan plans this spring to release a new monitor, so stay tuned for its review in an update to this test.

Bottom Line: The Raritan unit provides standard tank monitor features with external capacitance sensors. We found its tech support and website to be lacking.

The Scad Solo Profile Series (TM01) holding-tank monitoring kit includes a very small 2-inch-by-3.5-inch display panel, five feet of aluminum sensor foil, and one capacitance external tank sensor module. The display panel has a membrane-covered mechanical switch labeled “Read,” five prominent LED lights (that illuminate quite brightly) above each of which are labeled tank status levels (from empty to full) and a “Tank Full” red LED. It also has two tiny buttons (marked “F” and “E”) for calibrating functions.

Installation of the Scad Solo got off to a rough start due to its lengthy and unclear instruction manuals: a six-page booklet for the external non-contact fluid level sensor and a 10-page manual for the display panel. That seemed like a lot of reading for what should be a simple installation and hook-up. Upon digesting the instructions, testers found the manuals to be extremely wordy and not explicit enough. In fact, we had to call the manufacturer twice for clarification. Scad immediately e-mailed a new version of the instructions and offered verbal help.

Part of the confusion stems from the fact that Scad offers several versions of the display, and it can be programmed to work with many different types of tank sensor devices. The model we tested is intended for a holding tank. Scad also offers sensors specifically for water tanks as well as display panels that monitor up to eight tanks (Profile TM02).

In response to PS testers’ difficulty in translating the instructions, Scad said it is now overhauling the manual to make it shorter and more concise.

What the instructions lacked, the company makes up for in customer service. Technical support is available via phone seven days a week, 365 days a year.

Our initial problems aside, the installation and testing went smoothly. The Scad Solo Profile monitoring panel and external sensor have some unique and interesting features, including the ability to be calibrated for more accurate readings when using oddly shaped tanks that may be custom fitted. It also has the ability to program the characteristics of different types of tank sensors such as several internally mounted devices and the standard float sensors. Third, it allows you to program and set exactly where you want both the “empty” and “full” levels to be on your tank. Fourth, the external tank sensor module has a green LED indicator light that glows when the panel’s “Read” button is pushed, to indicate that all wiring is working. Finally, the Solo designed for holding tanks has a large red LED light on the panel, marked “Tank Full,” that will illuminate when the tank is 85 percent full. It reads the tank level every half-hour, so there may be about a 30-minute delay before the alarm goes off.

The Scad Solo will monitor only one tank, and the kit comes with one sensor and one display panel. To monitor two tanks, Scad suggests installing a rotary switch at the display panel, wiring it to sensors on the tanks and simply switching from one tank to the other as needed.

Bottom Line: Our favorite in the single-tank category, the Scad Solo kit was the most accurate, has more programming and calibrating flexibility, and will handle irregular-shaped tanks. We also like the tech support availability.

SensaTank Marine 100

The SensaTank Marine 100, made by TouchSensor Technologies and distributed by West Marine, says “Holding Tank Monitor” on the box but will work on freshwater tanks as well. This kit can monitor three tanks and contains three sets of fluid-level external tank sensors.

Each set has four proprietary stick-on “Mirus” field-effect detector cell sensors—one each for full, quarter-, half-, and three-quarters full—all pre-wired to a plug. This plug connects to the interface board presumably located near the tanks. The kit includes 20 feet of CAT-5 type cable and connectors to wire to the remote display panel. The 3.5-by-5.5-inch panel comes with screws and a plug for mounting and connection to 12-volt DC. The kit included an AMP male plug but did not include a female plug, and instructions suggested cutting off the plug to wire up to power. The panel has three field-effect touch-sensor buttons identifying “Tank 1,” “Tank 2,” and “Tank 3,” and an LED lighted bar graph that illuminates progressively to show the level of the selected tank when the corresponding button is pushed.

It comes with a very simple two-page instruction sheet with good diagrams. The installation is fast and straightforward with “plug-and-play” wiring that is obvious and intuitive with little chance of mistakes. No calibration is required. However, it would help if the detector cell sensors were marked: “full, ¾, ½, ¼.” (There is no “empty” sensor.) We accidentally stuck the quarter-full sensor near the bottom and the full sensor too close to the top. Once affixed, the sensors are very difficult to move.

Operating the monitor is very simple, and reading the level status is straightforward. Pressing and holding the button for the desired tank will illuminate LEDs behind cutouts that clearly show the liquid level. The SensaTank also has a visual alarm: If the tank liquid level reaches either below the quarter-full sensor or up to the full sensor, the indicator light flashes two times per second.

Bottom Line: SensaTank Marine 100, our top choice for the multi-tank monitor kits, comes with all necessary wire, connectors, and equipment, is easy to install, and simple to operate. The LED indicator lights are bright with easy-to-read labels, and the empty and full lights will flash when in alarm condition.

Acu-Gage Smart Mini

Another single tank monitoring kit, the Acu-Gage Smart Mini, manufactured by Snake River Electronics (now owned by Diamond Distribution), looks and functions almost identical to the Scad Solo.

The kit comes with a small display panel with stick-on ID stickers (“Fresh,” “Grey,” “Black,” “Waste,” and “Diesel”) for the single panel button, a holder for fuses and crimp connectors, a Moda capacitance sensor module, and five feet of aluminum sensor tape. The display panel includes five LEDs marked “Empty” through “Full,” tiny calibrating buttons, and a larger tank reading button. The 10-page instruction booklet was straightforward and well written—although like the Scad, it too had an incomplete wiring diagram.

While the Acu-Gage and Scad Solo look similar, their electronics and software are different. The Acu-Gage does not have an LED on the sensors, a “Tank Full” alarm/LED, or the ability to program different types of sensor or calibrate for odd-shaped tanks. The Acu-Gage monitors one tank.

Bottom Line: The Smart Mini is a no-frills kit that works well and is the least expensive, but it lacks extra features, and current availability through local marine distributors is lacking.

Acu-Gage three tank

We also tested Snake River’s three-tank monitoring kit. It has a larger monitor panel than the Smart Mini, but it calibrates and operates the same. It also has two additional tank push buttons.

Testers noted that accuracy was a bit off during testing, but Snake River suggested that adjusting the tape application slightly will alleviate this.

Bottom Line: This Snake River unit functioned without any problems, and it’s reasonably priced. We would like to see Snake River improve its tech support and presence in the marine retail market.

The quality and workmanship of all the display panels we tested appear to be good or better. The products are small enough to mount just about anywhere, and all draw minimal amperage.

The cost per tank monitored is difficult to determine since we tested both single- and multi-tank sensors. If you need to monitor two or more tanks, a multi-tank display makes sense and may even save you time and money. Each manufacturer represented offers additional tank sensors, and some offer other displays that allow for more tanks to be monitored.

Rating the sensors’ accuracy also was difficult, since each of the capacitance foil sensors read the tank water levels a little differently. When the tank was half full (visually measured), only one lit up half, while one showed one-quarter, and the others three-quarters full.

That being said, we decided against choosing a Best Choice and Budget Buy, and instead recommend the two standouts in this test: the Scad Solo single-tank monitor and the SensaTank 100 multi-tank monitor.

The feature-laden Scad was a top performer in accuracy with its main drawback being the instructions that are being revised, and the SensaTank was easy to install, accurate, and had good tech support.

• How We Tested
• Practical Sailor Value Guide: External Holding Tank Sensors

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Guides and tutorials for sea enthusiasts

[GUIDE] Installation of a black water tank for boat

• Comfort on board , Black water tanks

To be in good standing with the regulations on marine toilets , all boats built since January 2008 must be equipped with a black water tank. This is a tank specially designed to collect the materials coming from the toilet. Whether you have a motor boat or a sailboat, it should be equipped with a Marine toilet with tank . In most ports and anchorages in Europe, it is in fact forbidden to discharge black water within three miles of the coast. The ban on discharging black water in certain maritime areas is practiced almost everywhere in the world. To navigate in peace, it is therefore recommended to comply with the marine toilet legislation . So how do you successfully install a black water tank for a boat? In the rest of the article, find out everything you need to know.

The equipment needed to install a wastewater tank

Before starting, you must have the right equipment. First of all, choose a black water tank adapted to the space available on your boat and to your needs:

• See the rectangular black water tanks (the most common) - from 50 to 200 L
• See a vertical black water tank  
• See the truncated black water tanks - from 50 to 100 L

Then, you will need a macerator grinder:

• See the Osculati macerator grinder
• See the Jabsco macerator macerator

Note that there are black water tanks with integrated macerator. They are compatible with all electric and manual marine toilets:

• 60L 24 V horizontal tank
• 70L 12 V horizontal tank
• 72L 24 V vertical tank
• 80L 12 V horizontal tank
• 91L 12 V horizontal tank
• 91L 24 V horizontal tank
• 112L 24 V vertical tank

You will also need a black water tank hose . In addition, we strongly recommend the installation of a odor filter. 

Finally, the tanks never include a probe. To know the filling level of the black water tank, it is essential to install a meter connected to a gauge. The Osculati kit has the advantage of having both with a universal holder for tank from 15 to 55 cm high (the sensors of the probe must be cut according to the height of the tank used.)

The tools necessary for the installation of a black water tank

Before starting to assemble your fuel tank Manual or electric marine toilet , check that you have the equipment manual. It must also be stored in a waterproof pocket and placed within easy reach for consultation in the event of a problem. Take your toolbox because you will need all of its contents throughout the installation of the tank. Make sure you have all sets of flat and Phillips screwdrivers, along with a marker, cutter, and flex clamp pliers. You also need a drill with the bits, as well as a hole saw for drilling pipe passages. All the accessories delivered with your black water tank for boat must be complete. Take the time to check if all the connecting pipes, as well as the clamps that go with them are there. If you have to tackle the installation of a black water tank for boats of a particular design, provide the appropriate tools. Be aware that installing this equipment can take you four to six hours. It all depends on the complexity of the clean water inlet and black water evacuation systems.

The steps in the assembly of a black water tank for a boat

To install a black water tank for a boat correctly, it is necessary to study its location. This avoids a lot of inconvenience in the event of subsequent malfunctions. You absolutely have to anticipate how to empty the black water tank when it is full. The tank can be placed above or below the waterline depending on space availability. The first step in the installation is therefore to choose the right location adapted to the size of the tank. After having located the ideal place, the assembly of a black water tank for boat proceeds according to the following steps:

• Place the tank on its location using the fixing elements supplied by the manufacturer
• Screw the inlet and outlet caps of the tank
• Mark the passages of the pipes on each partition using a marker, taking care to calibrate the diameter of each pipe.
• Drill the pipe passages with the drill or using a hole saw
• Connect the vent and deck hoses
• Install the drain pump and the drain hose to the through-hull
• Connect the black water supply hose from the marine toilet

If the position of the black water tank is above the marine toilet, the installation of an anti-siphon elbow is recommended. The same is true if the bowl of your marine toilet and the tank are located below the waterline.

• See a 19 mm marine toilet anti-siphon elbow
• See a 25 mm marine toilet anti-siphon elbow
• See a 38 mm marine toilet anti-siphon elbow

To complete the installation of a black water tank for a boat, check the solidity of the connections and install the various accessories: gauge, non-return valves, anti-odor filters, etc. The tank assembly steps may vary depending on the marine toilet model installed on your boat . For install marine toilets electric, for example, you need to mount a pump 12v macerator or 24v between the bowl and the black water inlet of the tank. If you have a Marine toilet with macerator , you can skip this step.

Problems frequently encountered when installing a black water tank for boats

On a small boat it is common to find a toilet marin manual or a Chemical marine toilet which is not connected to a black water tank. If you plan to install a tank on board, the main difficulty is finding the location. Be aware that there are small capacity tanks on the market that you can place horizontally or vertically in a tight space. Many boaters also face some problems when fitting a new tank in place of used equipment. the dismantling a marine toilet and its reservoir risks, in fact, causing damage that must be repaired. As part of a replacement, take all possible precautions not to damage certain structures of your boat. If you feel that the installation of a black water tank for boats is a fairly complex task, do not hesitate to call a professional installer.

Our advice for maintaining a marine toilet black water tank

Once the waste water tank is installed, it must be well maintained. It is recommended to use in the black water tank of the  YACHTICON Purysan Ultra . It prevents the formation of unpleasant odors and breaks down feces and toilet paper.

In addition, it is recommended to clean the tank at least once a year before wintering. At this time, use  YACHTICON Puryclean  to clean and disinfect the black water tank. 

Learn more about marine toilets, chemical toilets and black water tanks:

MAINTENANCE: Cleaning a black water tank for boats

How to prepare the wintering of a marine toilet for a boat?

How to drain a marine toilet on a boat?

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How To Pump Out Your Holding Tank

Last Updated by

Capt Chris German

June 15, 2022

Everyone Poops. One of the grossest mysteries of owning a boat is what happens when it goes down. Where does it go? How long does it stay? And how do I get rid of it?

The subject of holding tanks and poop is one that is almost too difficult to broach in polite company. No one wants to admit they even do it, let alone what they do with it afterwards. So today, we pull back the curtain and look deep into the subject that is pooping on a boat.

Table of contents

The black water tank

I am not sure that it Is it any coincidence that the most well known private mercenary force responsible for countless war crimes shares the same name as the tank that holds the foulest of human byproducts.

Black Water.

The very term brings up secrets, unmentionables and private human functions. So I guess it makes sense that they share a name.

The black water tank on a boat usually has a nasty smell and as such is usually located under the least desirable bunk on the boat- usually under the vee berth.  It gets this smell not from your colon necessarily, but from the sodden, festering marinated combination of all forms of human effluence. This mixed with paper products, water and stirred exuberantly by the motion of the boat and left in an oxygen free environment for partial anaerobic consumption is to blame.

It is these anaerobic bacteria, combined with the bacteria of your lower bowel that create a truly odoriferous experience for anyone forced to sleep in the vee berth or tasked with the duty of emptying said tank.

The grey water tank

This is the tank that holds the washing water on a boat. The grey water tank  is a much less innocuous sounding facility and not all boats have them.  Some boats combine grey and black water into one tank, while others separate them. If your boat navigates exclusively in non-discharge zones along Coastal and Inland waters, you are required to collect all of the “grey”water.

 Grey Water by definition may contain no fecal matter. It may, however, contain bacterias and soap products that are noxious to the water environment and should not be discharged in bodies of water that do not intersperse readily with the world ocean environment.

The presence of these bacteria, (particularly if you are one who urinates in the shower) can make this water very smelly and almost equally gross as black water. Other things like food particles, dirty clothes and bath water also give this water a distinctly disgusting quality. As such, it  should never be dispersed on any human or animals consumed plants or food sources.  

The fresh water tank

This tank should never be confused with either of the previously mentioned tanks as this is water that can be consumed by humans and animals. It really bears no relation to pumping out the holding tanks other than while you are at the pump out dock, oftentimes there is a fresh water hose available for potable water that should never be used in any way with your holding tanks.

You may also find the fresh water fill on the deck of your boat in a similar configuration to your waste water and holding tanks. Please never confuse these two filling ports on your boat and if you do decide to fill your freshwater tank while on the pump out dock, be sure to use the spigot that says potable or drinking water and never cross-contaminate the hose.

How to use the pump out dock

In many places around the world, a dock that is designed exclusively for pumping boats out is available to recreational boaters.  You will know it is a pump out dock because it should have lots of signs on it. It will have a prominent fixture on it that has a two inch flexible hose coming off the side. It is  likely to have a yellow or black handled ball valve at its end with a sight glass on it.

Not every pump out dock is the same and sometimes you are charged a fee to use the pump out, but the best communities I have found have free pump out services for the public. In the places I have lived where I used the pump out, namely Connecticut, North Carolina and Utah, the systems are pretty universal.

When you pull up to the pump out, you will likely encounter other boaters. Be considerate. If you have a 24 foot boat, please don’t use slips where a 65 foot boat can only park. Also,  please don't park right in the middle of a dock if it can fit more than one vessel.

Pull your boat to the end, but not so far that the hose will not reach your boat. Use your best judgement, but please be considerate to others.

Once you're docked, now is time to pump. Take the hose off the pumpout housing and drag it to your boat. You should have a pump out fitting that screws into your waste hole on your boat. They come in 2 inch and inch and half  threaded sizes so make sure you have the right size for your boat. Unscrew the deck cap and put the cap in a safe place so you don't drop it overboard.

Now, screw the pump out fitting into your waste hole tight enough so that air cannot escape but not so tight that you can’t ever get it out. Next, take the ball valve with sight glass and fit it onto the lip of your pump out fitting. There should be two levers on either side of the valve that flip upward to secure the hose fitting to your pump out fitting. Once you have flipped those levers, you can turn the pump out on by pressing the green button on the pump out housing.

You will now hear a pump kick on and you can open the handle on the ball valve. You should see a brown or grey slurry get sucked up into the hose. Sometimes you may need to open and close the handle partially to establish the suction on weaker pumps.

The hose will then transport the fluids up to the housing and then pump it down the docks to a septic tank or sewer system on shore.

You will know you're finished when the pump out can no longer pull a steady stream of fluid from your tank by looking in the sight glass. Close the valve and unlatch the levers and pull the hose off of your pump out fitting. Place it in the water while you take the cap off your grey water tank and repeat the process.

When you have pumped both tanks dry, open the vale and place it back in the water. This will suck up sea water and flush any solids that got stuck in the line up into the system. Close the valve and neatly coil the hose back onto the hook on the pump out housing.

I like to use the hose that is designated for pump out to wash down the area and put a little fresh water into the tanks. You can repeat the pump out process if you want to get that rinse water out, but I find it dislodges solids over time so I like to leave a few inches of water in my tanks after I have pumped them out.

Now you can flush a sanitizing pouch, also known as a “blueberry”, into the tanks and be on your merry way.

The pump out boat

There is another service offered by some marinas and municipalities - a mobile pump out.  A pump out system is installed on a boat that can come directly to your boat on the dock or mooring. Sometimes this is a free service and other times it is pay service, but either way you should tip the pump out guy who drives the boat because it's a nasty job.

Many times the pump out guy will do all the work, but you really can help him by telling him if your boat is vented or not. Vented boats have a tube that vents out the side or through the cabin top that allows vapors to escape and prevents a vacuum from forming when you pump the tanks.

If your boat is not vented, you run the risk of imploding the tanks when you pump out, so you will need to open the traps in the toilet to allow air to come in while pumping out.  This goes for the pump out dock as well, but in my experience is much more important with the pump out boat because they generally have stronger pumps since they don't have to suck the fluids uphill to a facility.

Keeping you and your tank healthy

There are a few million infectious diseases in a holding  tank that can get all over the place when you are pumping out. Taking precautions like not touching your face, washing your hands, using hand sanitizer and using gloves should keep you safe. Some folks like to wear a face shield and apron when they use the pump out cause there is a chance that things can spray and get really nasty.

You can also minimize the colonization of bacteria in your holding tank by pumping it regularly and using additives that help break down the solids and decompose them into a more fluid consistency. One of our favorites is Happy Camper , an additive you mix with water and pour into your holding tank. It kills odors, breaks down solids and makes living with holding tanks that much more appealing.

Another thing you could do occasionally is wash out your holding tank with a multi-directional hose fitting. They are available online. We use a long rod to stir our tanks every once in a while in addition to the hose  to break clumps of paper products and chunkids.

There is also a theory that if you dump a couple bags of ice into your tank that the ice chucks will scour the solids from your tanks and help clean it out. I think this could work on a boat that is moored much better than one at the dock, but try and let me know how it works for you.

Finally, bleach will sanitize your tank but it also kills all the good microbes that help break down the materials in your tank. Once a season, I have been known to give my plastic tanks a good cleaning with bleach but I would never use bleach on a bladder or non-rigid tank for fear that it degrades the fabric.

Clogs will happen

It's a nightmare when it does happen, but clogs do occur. Usually it is because someone flushed something they shouldn’t have flushed and it gums up the tank or lines.

A key to preventing clogs, especially if you have young ladies on your vessel, is to make it clear to them that nothing goes in the toilet that hasn’t gone through your mouth first. Keeping a trash can nearby in the head helps enforce this rule. Some folks even resort to private shaming with a sign in their head that reminds their guests of this rule.

Whatever you do, keeping that stuff out of the tank is your first option. If it does get in there or you have a clog from some other way, there is not much to do to fix it but get manual. Don your face shield and gloves and go in to find where the clog is located and break it up.

Toilet paper is a big culprit when it comes to clogs so using fast decomposing paper is a good choice. Other ways it can happen is when your guests don’t use enough water to wash the solids down. If this is the case, you might be able to use a high pressure nozzle with your hose to blow the clog apart. Keep an eye on your sight glass to make sure you have washed the entire clog out of your tank and make sure you don't use that hose for any potable water purposes.

Pumping a boat out is a dirty business but we all have to do it. Taking care to keep your tank healthy and free of clogs will cut down on smells and make your vee berth that much better to sleep in. Don't be a jerk at the dock and if all else fails, ask your fellow boaters for a hand in learning how to pump your boat out. Most people are pretty nice when it comes to pumping out because no one likes to do it. Thanks for reading. Do good, have fun, and sail far.

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Capt Chris German is a life long sailor and licensed captain who has taught thousands to sail over the last 20 years. In 2007, he founded a US Sailing-based community sailing school in Bridgeport, CT for inner city youth and families. When Hurricane Sandy forced him to abandon those efforts, he moved to North Carolina where he set out to share this love for broadcasting and sailing with a growing web-based television audience through The Charted Life Television Network.

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• Falling foul: how to unblock the boat's waste holding tank

When returning our boat, the charter company technician informed me that the waste holding tank was blocked on our Sun Odyssey 43 DS yacht and that it would cost me 150 Euros to unclog it. I was a bit annoyed because unblocking a clogged black water tank is a 5-minute job. Of course, it's never a good idea to do this job in the marina or at least not in the daytime. But I told the technician that I would sort it out myself and it was a simple job. So, from my experience, I can tell you exactly how to do it.

How does the boat's waste holding tank get clogged?

Black water tanks clog regularly on older vessels. No toilet paper is allowed down a marine toilet and even though you may tell the crew this several times a day, occasionally someone will throw some paper in. The best way is to answer the call of nature in the sea. Take a leisurely swim far out to sea, fully relax as you do, and then casually relieve yourself. The bidet is all around you, so there's no need for toilet paper. Then swim back to the boat just as relaxed.

YACHTING.COM TIP: Did you know that a clogged toilet is one of the most common reasons for the boat charter company to take your security deposit? Find out what others are in our article — The most common reasons for losing your boat rental deposit . The truth is that taking out deposit insurance  will save your nerves and a lot of money, not just in the case of a clogged holding tank. So, what are the other benefits of getting coverage? Check out our 5 reasons to take out deposit insurance .

Check out more useful sailing tips:

The art of nautical map reading

Sextant and navigation: survival without GPS

The ultimate yacht cleaning kit

New Year's resolution: let's sail more eco

How to sail a yacht on a tailwind

How to sail a yacht in crosswinds

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Top 10 reasons boaters contact their insurers

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Anchoring in narrow bays, currents and swell

How to unclog a clogged toilet.

But back to the unclogging of the holding tank. So how do we do it? You need to grab a hose, get in the dinghy and paddle to the side of the boat to the pipe through which the tank leads out to sea. Insert the hose into the pipe (it is usually about 30 cm below the surface, so it is possible to do from the dinghy). Inserted the hose as far as it can go and mark how far it goes. Then take it out and wrap the hose with duct tape or electrician's tape so that the hose seals tightly in the pipe. Then just have one person on the dock by the water tap (where the hose is connected), and another in the bathroom by the shut-off valve from the holding tank.

YACHTING.COM TIP: Another thing our clients often ask is how the toilet (known as a 'head') works on a boat. That's why we've put together a guide on this topic — Marine toilet: how to use it . Take a look to find out w hat types of toilets you'll encounter on a boat, how to flush it correctly, what you shouldn't put down the head, how to avoid spilling the contents of the tank and how to deal with a blocked toilet.

And, what to watch out for?

So, I fed the hose into the underwater pipe from the dinghy and pushed the wrapped part tightly into the pipe to seal it perfectly. Then I called out to the dock, "Turn on the water!". I felt the water gurgling in the hose and heard the air bubbling in the waste tank. And then I felt some of the contents of the tank, pushed by the water from the hose like a plunger, shoot out through the vent valve located about a metre above my back, and some of the stinky contents fell in a very graceful arc onto my back, ran down my white T-shirt and onto my clean shorts. In an instant, I was covered in smelly excrement. Disgusted, I yanked the water hose out of the pipe and the fecal matter began to flow rapidly into the clear harbour water. The sea turned brown and I yelled, "Close the tank!". Paul, who was in the bathroom, shut off the valve in a flash and the brown patch stopped expanding. I discreetly sprayed water from the hose onto the patch, dispersing it further away from the boat. In a moment it had all but disappeared. The septic tank was unblocked and I smelt like fecal matter. I climbed on deck and met Jana who, as I passed her, backed away in absolute disgust and asked why I smelled so bad. So, I told her about my new special deodorant and headed to the shower.

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Marine Holding Tanks

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about boat holding tanks

Marine holding tanks are used for holding black water and grey water in boats, yachts, and sailboats. They are BPA free and rotationally molded with FDA approved polyethylene resin for potable water. Boat holding tanks are created by American manufacturer’s Ronco and Dura-Cast. Their rotationally molded design makes them crack resistant, durable, and long-lasting.

Capacities range from 5 gallons to 202 gallons, with thicknesses of 0.1875 inches (3/16") to 0.375 inches (3/8"). Both standard rectangular tanks and custom-molded tanks are available with pre-installed fittings or an optional DIY fittings package if buying a blank tank.

These holding tanks are new and can be used as replacement or new additions to vessels. They are designated for grey water or black water usage and should not be interchanged for potable water purposes.

Browse our manufacturer specific Ronco Marine Holding Tanks and Dura-Cast Marine Holding Tanks .

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Custom Plastic Marine Water Tanks and Marine Waste Holding Tanks (Freshwater, Grey Water & Wastewater)

At Miller Plastic Products, we manufacture custom marine water tanks to suit a variety of needs and applications. Many larger boats have a clean water system and a wastewater system. Clean water is also known as potable or fresh water; Wastewater is known as black water or gray water.

If there’s an RV or marine water tank available in stainless steel, or aluminum, we can fabricate the same shape and size container out of lighter-weight plastic materials, including:

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Request a quote for a custom marine holding tank from Miller Plastic Products below. These custom fabricated tanks start at $1,491.

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Our tanks are engineered using FEA (Finite Element Analysis) to maximize performance and allow for minimal bowing of the fabrication.

We offer a wide selection of custom plastic marine water tanks, marine waste holding tanks, and RV tanks in any size or shape to fit your need. Our tanks can also be heated for use in freezing weather. The kinds of marine tanks we can fabricate to your exact specifications include:

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Marine Water and Waste Systems

by Harbor Sailboats | May 9, 2022 | Blog | 0 comments

It goes without saying, boats are not connected to the sewer or water system like we experience at home. Instead, boats store, collect, and take in water for important onboard amenities. Boats have three types or “water systems”, fresh water, grey water, and black water. Let’s discuss how all three systems work.

Fresh Water- Fresh water is stored in plastic tanks built into the boat, commonly these tanks are under a bed or settee and can be anywhere from 10-100 gallons. On a modern sailboat, tanks are +/- 50 gallons and boats above 40’ have two or sometimes three tanks. Since the water tanks are at or below sea level, a 12 volt freshwater pump is used to pressurize the system and deliver water to the faucets as needed. This pump will come on when it feels the pressure drop below a certain level and turn off once the appropriate pressure is achieved. Without an onboard water maker or access to dock city water, these tanks are the only source of freshwater for extended trip.

Grey Water- Grey water refers to water after it has been used. The most common grey waters are from the sink and shower but any water source that is used in some fashion onboard is now considered grey water. For now, grey water is allowed to be drained directly overboard via the boats plumbing. As an example, sink water drains through a P trap and then exists via a thru-hull located below the drain. Sometimes two drains, like the sink and refrigerator, lead to a single thru-hull for reduced build cost and ongoing maintenance.

The other example of common grey water comes from the shower, but this water typically takes a slightly different path. Considering most shower drains are at or below sea level, it would be impossible for the water to use gravity to exit the thru-hull like the example above. Instead, most boats will have a dedicated shower pump the turns on and evacuates the water collecting at the bottom of the shower. Some boats will have an automatic pump with a sensor while others may have a manual switch.

It’s good to keep in mind that everything you put down the drain leads directly to the ocean.

Black Water- Black water comes from the head and simply put… is sewage. Unlike grey water, black water can only be discharged from the boat in certain situations. When the head is flushed, it goes through a hose and eventually makes its way to the black water tank or holding tank. Traditionally, the waste would first pass through a Y-value or diverter value that would send the waste to the holding tank or to the direct overboard thru-hull. That said, it’s common to now see gravity holding tanks that do not require a Y-valve. Explanation of both coming below.

In the US, it is legal to flush black water into the sea given you are more than three miles from any point of land. In this case, one could simple direct the Y-valve to the overboard position, open the head overboard thru-hull, and use the head. If your boat has a gravity holding tank, you simple open the tank outlet thru-hull and the waste will go from the head, straight thru the holding tank and overboard.

Since you are allowed to pump directly overboard while three miles offshore, you are also allowed to empty your holding tank of all waste. If equipped with a gravity tank, you simple open the valve at the bottom of the tank and gravity will take the waste and empty it overboard. If you are equipped with a traditional Y-valve and macerator, it works a little different. In this set up, the holding tank will have a hose that leads to a macerator pump and then to an overboard thru-hull. One would open the overboard thru-hull and engage the macerator pump to empty the tank.

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18 Gallon V-Shaped Boat Water/Holding Tank - WH-2018

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18 Gallon V-Shaped Water & Holding Tank  

Tank Dimensions 24.5″ L x 20″ W x 10″ H

These water tanks are suitable for the storage of potable water, freshwater, and wastewater (grey water, black water).

Trionic water and wastewater holding tanks are rotationally molded into durable, seamless, one-piece, non-corrosive tanks.  Each tank fully complies with FDA regulation 21 CFR 177.1520 and meets all U.S. Coast Guard regulations. Each Water/Holding tank has (2) 1-1/2″ FPT and (2) 1/2″ FPT threaded openings. Openings on all tanks feature female National Pipe Threads (NPT) and are located on one end of the tank. Unused openings can be capped. 

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V shape is ideal for fitting into the bow of some boats - Boat Bow Tank

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Custom fitting locations are available on orders of at least 5 tanks.

All Trionic Corp products offer a one-year warranty covering materials and workmanship.  Warranty does not cover misuse or abuse of the products.

This same tank is also available as a blank tank without the threaded openings.  These tanks allow the user to locate openings in the exact locations dictated by their installation requirements.  Trionic Corp’s CF-60 Custom Fittings kit makes the installation of a blank tank quick and easy.

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18 Gallon V-Shaped Blank Water/Holding Tank - B-2018

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Boat Holding and Waste Tanks

Whether on the water in your boat or on the road in your motorhome, quality holding tanks and holding tank systems are essential to your plumbing system. Polyethylene tanks are sturdy, keeping wastewater (black water and gray water) where it belongs: out of sight (and smell). Check out Great Lakes Skipper's amazing discount prices on marine waste tanks and holding tanks, hoses, holding tank monitors, and more wastewater tanks, holding tank components and accessories by Bayliner, Raritan, MPI, Dometic, and more top brands.

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Technical maintenance

Black water systemes: problems and solutions!

There are various water systems on a boat, including black water systems (wastewater from the heads). It is not a subject that people talk about that much, but dealing with black water can be a real headache.

March 3, 2023

There are various water systems on a boat, including black water systems (wastewater from the heads). It is not a subject that people talk about that much, but dealing with black water can be a real headache. It is a delicate but essential matter. If you have a weak stomach, read no further!

The first thing to understand is that the heads on a boat are systems that grind up and eliminate wastewater. As everyone will tell you, when it comes to toilets, prevention is better than a cure! With this in mind, here are a few basic rules for correct use.

First of all, be extremely careful about what you dispose of in the system. You should only use specially-adapted toilet paper. Next, always clean the heads with special eco-friendly products. Do not use any products containing acetone, trichloroethylene, or any other product that can damage rubber parts.

UNDERSTAND HOW THE SYSTEM WORKS

To keep the system in good working order, it is essential to understand the mechanisms involved.

There are two types of toilet:

• Manual toilets, which you have to pump by hand to create suction to flush.
• Electric toilets: simply push a button to activate the inlet of freshwater into the bowl and flush away the black water.

In some navigable waters, you are advised not to discharge black water into the sea, and indeed prohibited from so doing in some regions. There are two ways to empty out your toilets: either have them emptied by a company specialized in doing this in port, or discharge black water into the sea (provided that this not prohibited). Even so, out of respect for everyone, you MUST discharge black water in offshore waters, at least six nautical miles from the coast.

In practice, when you flush the toilet, the black water is pumped into a black water tank. If the outlet valves are closed, then the black water remains in the holding tank.

You can prevent disaster by following a few simple rules:

• To keep the hull outlet valves, connected to the heads, in good working order, you should open and close these valves (concealed under the sole) at least once a month.
• If you are offshore, in a zone where discharging black water is allowed: rinse out the tank as often as possible, by opening the valves, filling the tank (using the deck filler) with freshwater and pumping it out via the through- hull outlets. It is advisable to take the boat out of the water once a year and clean all the through-hull fittings.
• If you are in waters where the temperature is below zero, you should also drain the black water system to prevent water in the pipes from freezing. Use of antifreeze is not recommended, since it is not compatible with the system.
• Lastly and most importantly, drain your black water system before leaving your boat. Also remember to flush the system through using freshwater (never seawater) so that your system will contain only clear water. If you fail to do this, the black water will dry out, block the pipes and damage the tanks, and your boat will reek of bad smells.

Should your toilets ever become blocked, it could be for one of several reasons: there may be something blocking the grinder, or blocking the manual pump or your through-hull may be blocked. If you want to repair the system yourself, then certain precautions should be taken, including closing all valves connected with the heads, and cutting off the water, to carry out the repairs safety. You can dismantle the grinder, and its motor if necessary, to remove whatever is causing the blockage. If you have manual toilets, you can dismantle the pump.

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Black Water Tank Smell

• Thread starter Plymouth Sailor
• Start date Mar 3, 2022
• Tags head odor toilet
• Forums for All Owners
• Ask All Sailors

Plymouth Sailor

Fellow sailing brethren, I recently upgraded to a larger sailboat with a full head and black water tank (I’ve only dealt with a porta potty in the past). A smell is emanating in the boat and I would gather it‘s not directly from the tank as it’s sealed but rather from the head. This seems to be an old head. Are these marine toilets suppose to have either an elbow in the piping and/or a flap to stop the gas/odor from escaping? Also, any suggestions on the best chemicals to use?  

The smell is probably coming from the hoses. Old hoses permeate with the odor. The best hose is Raritan Saniflex, not cheap but it works. To test the hoses, put a wet rag on the hose for a few minutes and then smell the rag. The best price on hose is at Defender, only about $10 a foot. After trying many products the one I found that works best is Camco's TSP. It comes in both a liquid and powder form and is among the most economical products available on Amazon and RV Camping stores. If you don't have it yet, get @Peggie Hall HeadMistress book, available here in the SBO shop.  

Scott T-Bird

It will take a while to get rid of the smell. I've found on both my boats so far that you have to replace ALL the hoses and the toilet to get rid of the smell. Don't neglect to replace the ventilation hose. There is no substitute or remedy other than total replacement. The tank is usually pretty hard to replace. Empty it and flush it as much as you can. Just keep flushing clean water through the tank. I was tempted to believe that the plastic tank was permeated with smell but I found that the outside of the tank is not and if you keep the ventilation open to the exterior, the smell from the interior of the tank will not be a problem. Once you get rid of EVERY hose and the toilet, you will find a big improvement. I even replaced the macerator pump, not because it failed, but because I think it was permeated with smell. (I basically replaced every single component and fitting in the entire system except the tank in both instances. But you will also find that the cushions are permeated with odor. You may not be satisfied until you treat or replace the fabric and even the foam. I replaced the cushions on my first boat right away. On my Catalina, we're working with the original cushions in the saloon because the smell is tolerable. We replaced all cushions in the v-berth and aft berth just because we are pretty averse to pre-owned furnishings. The saloon cushions aren't perfectly non-odorous yet. (We are very particular) Toilet odor is not easy to eliminate from a boat. Be patient and persistent. You will eventually rid the odor but it takes an effort and as much ventilation as you can introduce. P.O. on my Catalina had an in-line ventilation filter that he installed in the closet of the aft berth ... that was a huge source of smell! Don't even think about using one of those things!  

Peggie Hall HeadMistress

As others have said, permeated sanitation hoses are one of the most common sources of odor INSIDE the boat. However, if the odor is only emanating from the toilet, it's most likely due to the dead and decaying micro-(and not so micro) organisms in sea water that's been left to sit and stagnate in the toilet intake line, pump and the channel in the rim of the bowl. The cure is relatively simple, but depending on the make-model age of your toilet and the system hoses, it may make more sense to replace both. How old are they? And what's the make-model of your toilet? There is a one-way valve (it's called a joker valve) in the toilet discharge fitting that, when seriously worn, can allow gasses from the tank to escape into the bowl. But replacing that is not the cure for the odor--which venting to encourage adequate air exchange and the right type of tank product can preventfrom occurring. I'll be glad to help you learn how to do that. Others have recommended you get a copy of my book(see link in my signature below). I can't argue with that advice! It's title (my publisher's idea) is a bit misleading...'cuz although it does deal with every source of odor on a boat and how to cure, or better yet PREVENT 'em, it's actually a comprehensive "marine toilets and sanitation systems 101" manual that explains the laws, describes all the types of systems and how they work, and will help you learn how to operate and maintain your system to prevent 99% of problems instead of having to cure 'em. 'Cuz you get to do any preventive maintenance on your terms when it's convenient...the need to cure a problem never happens when it is! And btw...I see you're in Plymouth. There's at least one Plymouth in the US and at least one more in the UK and possibly one or more in other countries. Where are you? --Peggie  

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Better Sailing

Sailboat Water Tank Size

Similar to the gas tank, the water tank is also a vital component of your sailboat’s systems. A water tank can be used to hold wastewater, freshwater, and wash water. In other words, water tanks are your sailboat’s plumbing system and they supply water to the shower, galley, and even for electric toilets. Water tanks can be made of different materials like polyethylene, stainless steel, and plastic coated fabric. As for their position, they are usually safely situated somewhere inside the sailboat or they might also be portable. So, let’s see the characteristics and different uses for a water tank as well as its size.

General Info About Sailboat Water Tanks

Firstly, as we know water is heavy so it’s safer for water tanks to be situated low in the sailboat. But in case you want to add more water tanks, you’ll need to have a relatively large sailboat in order to provide some extra space. In the market, you can find many different sizes and shapes of rigid polyethylene tanks. A water tank normally has three threaded ports, one for the outlet, one for the vent hose, and one for the fill hose. Threaded hose barbs are used for hose connections. The inlet is connected to an on-deck fill and the vent line leads to a vent fitting high in the sailboat.

Keep in mind that if the vent is not higher than the fill, then it might overflow when you are filling the tank. Furthermore, remember that the outlet connection leads directly to a pump or to a manifold/Y-valve for a multi-tank installation. Finally, remember to secure hoses with stainless steel hose clamps.

Water Tank Position

Water tanks can be usually situated on each side of the sailboat or on its center in order to keep it balanced. When their location is on each side of the sailboat then they are connected together with a balance pipe of approximately 1-inch in diameter. This way both tanks are kept at the same level. Keep in mind that in case the balance pipe is small then it might take more time to fill in. This happens because the transfer of the water from one tank to the other is difficult to happen quickly enough. In fact, when the two tanks are situated at the same height then your sailboat has a balanced system that requires only a one-level indicator.

Water Tanks Materials

Different materials can be used to manufacture water tanks. These can be stainless steel, polyethylene, aluminum, and flexible fabric. When it comes to measuring the pros and cons of these materials, everyone has its own characteristics. For example, polyethylene water and waste tanks don’t usually retain odors, compared to tanks that are made out of stainless steel or aluminum. On the other hand, stainless steel tanks are less prone to rust or corrosion problems but their cost is relatively high than polyethylene tanks. As for their construction water tanks have baffles that prevent excessive movement of the water inside. However, the in-between spacing depends on their construction materials. For instance, a Tek-Tank polyethylene tank will have a baffle spacing of approximately 250mm and 350mm. But, a stainless steel water tank usually has fewer baffles with a spacing of 500mm.

Tank Fittings

The hose that is used in order to connect the fill point on the tank to the deck filler can be of two kinds. Either a green-tinted delivery hose or a clear braided hose. The vent pipe and feed have usually a very small diameter, around ½-inch. This diameter suits the best for pumps and deck fittings. As for the hose tails which are basically the fittings connecting to the hoses; they’re barbed so that the pipe won’t come off. Therefore, the hose is pushed into the hose tail and then tightened with a jubilee clip. You can also use thread sealant or Teflon tape on all threaded fittings. Moreover, remember not to overtighten fittings in plastic tanks.

Water Tank Size

Let’s now see some examples of water tank sizes on different types of sailboats:

• The Bavaria Cruiser 34 has a 39-gallon water tank capacity.
• The Hunter 32 Vision has a 50-gallon water tank capacity and the tank is located under the V-berth.
• The Catalina 310 has a 55-gallon water tank capacity
• The Beneteau Oceanis 51.1 has a 106-gallon water tank capacity, located under the berth in the forward cabin.
• The Sparkman & Stephens 52ft Yawl has 2 stainless steel water tanks installed beneath the saloon sole. Each one has a capacity of approximately 50 gallons. 
• The Bavaria C45 has a 143-gallon water tank capacity.
• The Island Packet 38 has an aluminum 157-gallon water tank situated under the sole.
• The Amel 50 has a 160-gallon water tank capacity.
• The Hallberg-Rassy 64 has a 331-gallon water tank capacity.

The size of a water tank in a sailboat depends on different factors. Mainly, the model and type of your sailboat, its plumbing system as well as the tank’s materials, position, and construction . There is a wide range of sailboat water tanks available on the market for drinking water, wastewater, or where space is not enough, flexible water tanks. The most common materials are polyethylene, stainless steel, and aluminum. Moreover, there is a variety of shapes and capacities, ranging from 40 to 400 gallons . Keep in mind to drain water tanks of any waste or water when preparing your sailboat for off-season storage. Like this, you’ll prevent any unexpected damage by freezing temperatures. Last but not least, do not consider using any tank that is not easy to pump out.

Peter is the editor of Better Sailing. He has sailed for countless hours and has maintained his own boats and sailboats for years. After years of trial and error, he decided to start this website to share the knowledge.

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