Marine toilet: how it works, manual or electric, maintenance and faults

The Marine toilet is one of the onboard systems that breaks down most often and is repaired worst while sailing. It works with seawater drawn from a hull intake and discharges overboard or into a collection tank, so every installation error turns into bad odors, water rising back into the bowl or, in the worst case, a leak. Here we explain how it works, when a manual or electric model is convenient, how pipes and siphons should be installed, and which checks prevent the most common failures.

How the marine toilet works

A manual marine toilet has a double-acting piston pump mounted next to the bowl. With the lever in the wash position, each stroke of the piston draws seawater from the hull intake and sends it into the bowl, while the same stroke pushes the contents toward the discharge. Moving the lever to the emptying position closes the water inlet and the pump works only on the outlet, so the bowl stays empty and does not overflow when the boat heels.

In electric models, the hand pump is replaced by a motor with two functions: an impeller that brings washing water and a macerator that grinds waste before pushing it into the discharge pipe. Just one button and the discharge passes into a thinner pipe, because solids arrive already ground. Some models use fresh water from the onboard autoclave with a solenoid valve, instead of seawater: no odors caused by stagnant seawater in the pipes, but more consumption of the tanks.

If you are considering the entire bathroom area, with sink, shower and tanks, you will find a broader overview in the guide on how the bathroom works on a boat.

Manual or electric toilet: which to choose

The choice mainly depends on how much power you have onboard and who will use the bathroom. The practical differences are these:

• the manual does not consume electricity and is repaired with a gasket kit, but requires a few dozen pumps and a minimum of habit by guests;
• the electric is convenient and more hygienic, consumes power for a few seconds at each flush and needs a properly sized cable and a dedicated fuse;
• the electric with macerator allows longer discharge pipes and tighter curves, useful when the tank is far away;
• the manual suffers less from dirty seawater or algae, while a macerator blocked by a foreign object stops until you dismantle it.

Among the manual models you find the Jabsco 2008 manual WC pump. For the electric there are the Jabsco 37010-3092 electric toilet and, for those who want a high home-style bowl, the Tecma Compass High Toilet 24 V. If the bowl is in good condition you can convert the manual with a kit, like the Osculati 50.205.32 12 V electrification kit or the Trem Z1800040 12 V conversion kit. For a more detailed comparison between electric systems there is our guide to Electric toilet.

Installation: pipes, siphons and sea intake

The most common manual toilets use a 19 mm inlet pipe and a 38 mm internal diameter discharge pipe. The pipe must be chosen reinforced with spiral and smooth inside, fixed on every hose holder with two stainless steel clamps. The shorter the path, the less effort the pump makes.

The critical point is the siphon. If the bowl is near or below the waterline, seawater can enter by siphon effect even with the pump off and flood the area. technical sheet of Jabsco manual toilets gives precise rules:

1. on the inlet pipe, with the toilet below the waterline, install a 19 mm vented siphon with the highest point at least 20 cm above the highest possible waterline, between the pump and the bowl;
2. if the toilet always remains above the waterline even with the boat heeled, a 19 mm non-return valve near the sea intake is enough;
3. on the discharge towards overboard, with the toilet below the waterline, a 38 mm vented siphon is needed, always at least 20 cm above the waterline;
4. with the toilet above the waterline it is enough to form a loop in the discharge pipe at least 30 cm above the outlet elbow.

As a spare for the discharge you can find the Jabsco 38 mm siphon valve. Also remember to close the sea intakes when you leave the boat: a siphon that blocks with the boat unattended is one of the classic causes of flooding in the harbor.

Overboard discharge or black water tank

The international MARPOL rules on black water discharges apply to ships on international voyages of 400 gross tons and above or certified for more than 15 persons. For those ships, as explained on the’IMO page on black water discharges, treated and disinfected sewage can be discharged beyond 3 miles from the coast, untreated sewage beyond 12 miles and while underway.

For recreational boating, local ordinances of the Coast Guards and regulations of marine protected areas are especially important, which prohibit direct discharge in ports and near the coast. For this reason many boats have a collection tank with a three-way valve: in port discharge into the tank, offshore and where allowed empty overboard. If the tank is far or higher than the toilet, a Osculati 12 V macerator 50.220.12 helps to empty it or to push the discharge over long distances.

Maintenance of the marine toilet

A marine toilet lasts a long time if you treat it like a pump and not like a home toilet. The manufacturers' instructions, like those in the Jabsco sheet, are these:

• only toilet paper goes in the bowl, preferably nautical type that disintegrates quickly: wipes, pads, cotton and chewing gum block valves and macerators;
• after each use pump enough to completely empty the discharge pipe and leave the bowl empty;
• no acetone, bleach or aggressive detergents, which dry the seals and crack plastic parts;
• after long periods of inactivity lubricate the pump by running warm water with a specific lubricant for marine toilets;
• at the end of the season empty pump and pipes, or circulate a non-toxic antifreeze if the boat remains in water in cold areas.

Once a year it is advisable to replace the pump seals: for the Jabsco 2008 there is the complete repair kit, while if the leak is between the pump and the base, the’seal ring for toilet 2008.

Signs not to ignore

The lever is stiff or returns back

Usually the piston is dry or the seals are swollen. A specific lubricant solves mild cases; if the problem returns after a few days, it's time for the seal kit. A lever that suddenly becomes stiff can also indicate a blockage in the drain or limescale deposits in the pipe.

Water rises in the bowl

The ventilated siphon is missing, installed too low, or its valve is blocked by salt and limescale. It must be cleaned or replaced immediately, because it is the same defect that can cause flooding when the boat is stationary.

Bad odors in the bathroom

The most frequent causes are seawater stagnant in the pipes, with decomposing organisms, and old drain pipes that become permeable to odors. The classic test is to rub the pipe with a warm damp cloth and smell it: if the cloth smells bad, the pipe must be replaced.

The electric WC does not fill with water

Check in order the open sea intake and its filter, the fuse and the connections of the wash pump, then the impeller. On freshwater models, check the solenoid valve and the pressure of the autoclave. If the motor runs but water does not arrive, often the impeller is worn or the pump has lost its prime.

Spare parts, pumps, conversion kits, and accessories are collected in the category Marine WCs and accessories. If you don't know which seal kit your WC uses, send us the brand, model, or a photo of the pump and we will indicate the right spare part.

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