Marine toilet blocked, pumping badly or smelling

A boat’s toilet has nothing in common with the one at home: a small pump draws in seawater to rinse the bowl, then sends everything through a narrow hose, past non-return valves, to a holding tank or to an outlet through-hull. That whole path scales up, wears and holds on to smells. Most faults have an ordinary cause and can be sorted out without taking much apart; a few call for a professional. Your toilet manufacturer’s manual always has the last word, especially for the lubricant and the spare parts.

1. What you notice

• The pump gets stiff, the handle forces and the bowl empties poorly.
• The water comes back into the bowl after pumping, or the bowl fills up on its own.
• The bowl no longer fills with flushing water.
• A rotten-egg smell at the first pump after a few days away.
• A permanent smell in the heads compartment, even with a clean bowl.
• An electric toilet that runs without emptying, makes an unusual noise or blows its fuse.
• A leak around the pump or under the bowl.

2. Safety first

On a toilet that discharges overboard, two through-hulls are usually below the waterline: the seawater intake and the outlet. A hose that comes off or a seacock that breaks means water coming in. Close both seacocks before taking anything apart, and if a seacock refuses to close, do not force it: that is a job for a professional, preferably with the boat ashore. Black water contains germs: gloves, glasses, and wash your hands. A holding tank can give off gases: ventilate, and no flames nearby. Finally, never use a strong acid (such as hydrochloric acid) in the circuit: it attacks seals and valves and gives off dangerous fumes, and mixed with bleach it produces a toxic gas. Never mix two products.

3. The probable causes, from most to least common

• Urine scale — urine and the lime in seawater form a hard deposit that gradually narrows the discharge hose and seizes the valves. The pump gets stiffer little by little, over weeks or months. This is the most common cause.
• Worn or scaled valve — the rubber non-return valve (often duckbill-shaped) deforms, hardens or no longer closes: water comes back into the bowl and pumping loses its efficiency.
• Unsuitable paper or a foreign object — too much paper, thick paper, a wipe, a sanitary product or a cotton bud is enough to block a narrow hose. The blockage happens all at once.
• Closed intake seacock or blocked strainer — the bowl no longer fills; also check the position of the pump lever (flush or dry bowl) on models that have one.
• Holding tank full, wrongly switched or badly vented — the valve that sends waste to the tank or overboard (Y-valve) is in the wrong position; or the tank vent (a small hose that comes out on the hull or deck) is blocked by salt, an insect or a saturated charcoal filter. The pump forces, and smells come back out through the bowl or the vent.
• Stagnant seawater in the circuit — the rotten-egg smell at the first pump often comes from here, not from the black water: the small marine organisms left in the intake hose die and decompose. Unpleasant, but not a fault.
• Hose permeable to smells — over the years, many hoses let smells through their wall. A permanent smell with a clean bowl often comes from this.
• Worn pump — piston seals, a leaking shaft seal, a sticking handle: a manual pump needs its seal kit from time to time.
• Electric toilet fault — macerator jammed by an object, voltage too low (flat batteries, cables too thin), fuse, faulty flushing pump or solenoid valve.
• Blocked outlet through-hull — shells and deposits can narrow the outlet on the hull side; rarer, and mostly seen at haul-out.

4. What you can check yourself, safely

• The intake and outlet seacocks are open (and the pump lever is in the right position).
• The Y-valve is set the right way, and the tank gauge does not show it as full.
• The tank vent, outside, is neither blocked nor crushed; a charcoal filter on the vent is replaced as the manufacturer says.
• The rag test: rub a hose with a damp, warm cloth, then smell the cloth. If it smells, the hose has become permeable and will have to be replaced.
• White vinegar: pour some into the bowl, pump just enough for it to fill the hose, leave it to work for a few hours or overnight, then rinse thoroughly. Done regularly, it slows the scale down; on a hose already heavily scaled, it works no miracles.
• For an electric toilet: look at the fuse or the breaker, and at the battery voltage while the toilet is running.
• If you are comfortable and equipped, seacocks closed, gloves and glasses on, you can replace the valve or the pump seal kit following the manufacturer’s instructions. Have a bucket and rags ready: it is rarely clean.

5. When to stop and call a professional

Call a professional if the discharge hose is so scaled that it stays blocked (it is replaced rather than cleared), if a seacock is seized or leaks, if a through-hull is weeping or corroded, if the smell persists after the hoses have been replaced, or if the tank, its pump-out pump or its sensor are involved. The same goes for an electric toilet that does not start again once the power supply has been checked. Describe what you noticed: how stiff the pump is, water coming back, the kind of smell, since when.

6. Stopping it from coming back

Little paper, and nothing but paper: a small bin nearby avoids most blockages. Pump enough each time for the water to travel the whole hose, all the way to the tank or the through-hull. Before leaving the boat for a few days, rinse the circuit with fresh water to avoid the rotten-egg smell, then close the seacocks. Work every seacock at least once a month so that it does not seize. A regular dose of white vinegar, a spare valve and seal kit on board, and a check of the hoses at winter lay-up (see winterising and recommissioning) complete the maintenance. As for discharges, find out the rules where you sail and at your marina: many forbid any discharge in harbours, anchorages and near the coast.

In the Hullteam log, record the replacement of hoses, valves, seals or seacocks, with the date and the part references: that is what will make the boat’s value at resale, because a buyer knows what redoing a toilet circuit costs (see which proofs count).