How can I stop air entering my marine toilet system?
My seawater-flush toilet splutters and takes several strokes to draw water after it has been left overnight. Once it gets going it flushes reasonably well, and I cannot find any water leaking out. Where should I look for air getting in?
Answer
To stop unwanted air entering a seawater-flush marine toilet, check the inlet hose connections, strainer lid seal and pump inlet valves first, as a suction leak can admit air without leaking water out. Keep anti-siphon protection working: it deliberately admits air to prevent seawater siphoning into the boat.
Identify the air entry point
First establish whether the toilet draws too little flushing water, struggles to discharge waste or has a vacuum pump that runs repeatedly. Each points to a different fault. Replacing the discharge valve will not normally cure a pump that cannot draw seawater.
Close the relevant seacocks and isolate electrical power before disconnecting hoses or opening the toilet or pump.
- Spluttering flush water or lost prime after standing: suspect the seawater suction hose, strainer seals or pump inlet valves.
- A stiff handle with little incoming water: check for a blocked intake, clogged strainer or restricted hose before assuming an air leak.
- Waste returning to the bowl: inspect the discharge non-return valve, often called a joker valve, and check for discharge restrictions.
- A vacuum toilet cycling while unused: investigate the bowl seal, vacuum pipework and vacuum pump valves.
Air passing through the discharge during dry pumping is normal. Assess the fault by checking that the toilet draws water reliably, clears the bowl and stays idle afterwards.
Check the seawater inlet
Inspect the whole suction run from the seacock to the pump. Many small yacht toilets use approximately 19 mm inlet hose and 38 mm discharge hose. Check the hose markings and fittings before buying replacements.
- Clean the strainer. Remove weed and grit, then clean the lid groove. Check the O-ring for flattening, splits or twisting, and fit the correct replacement seal if damaged.
- Inspect hose ends and fittings. Look for hardened hose, cracks beneath clamps, loose tails and cracked plastic elbows. A joint under suction can draw air while staying dry outside.
- Check the clamps. Position them over the supported hose tail, behind its retaining bead where fitted. Replace corroded clamps with suitable marine stainless clamps. Overtightening can distort hose or crack plastic fittings.
- Check the hose route. Remove kinks and investigate unnecessary high points where air can collect. Replace hose that collapses when the pump operates.
Use seal lubricant only where the manufacturer permits it, and check that it is compatible with the rubber. Do not smear sealant around the outside of a suspect joint. Dismantle it and repair the sealing surfaces.