How does a marine toilet really work?

How does a marine toilet really work?

Peculiar topic but extremely practical. If you've already been on a boat, you know what we're talking about!

by Francesco Gambini

A boat's toilet doesn't look substantially different from a domestic one. It's slightly smaller with a porcelain bowl and a seat. Due to the limited space, it is usually used while seated. If you choose to spend a few weeks on a sailing boat, it is essential to be familiar with it.

How does a marine toilet really work?

The main feature of a boat's toilet is that it flushes directly into the water. As it is below the boat's surface, there's a hole in the hull through which its contents have to be pumped out.

This operation may be a little scary the first time, but it is not difficult at all. Knowing what to do can avoid causing damages to your boat: it is a rather delicate piece of equipment, if not used correctly. Nautical toilets have a pump, electric or manual, and a diverter tap that manages and directs the flow. Basically, after use, you'll flush the contents of the bowl outside while continuing to flush the bowl.

Some rules of etiquette

For safety reasons, the diameter of the pipes is smaller than that of domestic pipes, which is why it is essential to use the toilet only for its intended purpose. There is a small external container for toilet paper. My personal recommendation is to be careful not to throw bigger objects or small pieces of food inadvertently.

How to operate the marine toilet pump

In the case of a manual pump, this involves repeatedly moving a piston back and forth via a knob, while in the case of an electric pump, this function is carried out by an electric motor. There are also automatic electric toilets where these operations, including the pump flow diverter, are handled automatically for an experience of use similar to that of ships or planes.

Consider that an electric toilet is relatively noisy, so at night I suggest, if possible, using a boat toilet equipped with a manual pump model.

If the pump is a bit hard, you can lubricate it without dismantling anything by pouring a little oil into the bowl and then pumping.

I recommend, for example, the oil from a tin of tuna which is ideal for this purpose.

The holding tank

More and more boats are being equipped with a holding tank to hold the toilet to avoid direct discharge into the sea. A holding tank has multiple benefits. With it, you'll be able to use the boat's toilet whilst:

  • in a harbour where it would otherwise be wrong to discharge (the water has a limited circulation and would be irreparably contaminated)
  • on a roadstead, so your crew can continue enjoying their swim undisturbed  
  • in the proximity of nature reserves where discharge into the sea is prohibited

Keep in mind that on a boat equipped with several toilets, not all of them have a black water tank; it is usually located near the toilet, inside some cabinet and has a volume of about 40 litres, so check which toilets are equipped and behave accordingly.

Sometimes, particularly in hot weather, it can give off unpleasant odours: to avoid this, first of all, remember to keep it empty as much as possible, emptying it as soon as possible and with the contents significantly diluted, and washing it by pumping empty seawater from the bowl could help. For more stubborn cases, it is generally fitted with an opening with a plug on the deck, similar to taking on water, through which hot water can be introduced to facilitate the operation. It can also be emptied through this hole in the port using a machine that sucks out the contents (in the few ports which are equipped with one).

This post is written by Francesco Gambini. Francesco met sailing in Liguria 20 years ago. A fleet specialist in Sailogy, his favourite boat is the Dufour 310 Grand Large. 

Francesco Gambini