Why does my boat toilet smell, and how do I fix the odour?
I've got a horrible rotten egg smell coming from the heads compartment on my 2008 Beneteau. I've tried scrubbing the bowl and pumping lots of bleach through it, but the smell comes right back a day later. What is causing this and how do I actually get rid of it permanently?
Answer
A marine toilet smells because hydrogen sulphide gas is either escaping through degraded sanitation hoses or venting back into the boat from a blocked holding tank. To eliminate the odour permanently, you must replace permeated hoses with high-grade butyl rubber, unblock the tank vent, and stop leaving stagnant seawater in the bowl.
The Hot Damp Cloth Test
Test your hoses before ripping the plumbing apart. Wrap a hot, damp cloth around the lowest section of the 38mm (1 1/2 inch) black water discharge hose. Leave it for two minutes. Remove the cloth and smell it. A sewage smell means the hose has permeated. Standard PVC sanitation hoses break down after five to seven years. Uric acid and gases leach directly through the pipe wall.
Replacing Hoses with Butyl Rubber
Bleach and air fresheners cannot fix permeated hoses. You must replace the pipework. Avoid cheap PVC sanitation hose at £10 a metre. You will just repeat the job in three years.
- Buy a premium butyl-lined hose like Raritan Sani/Flex or Vetus Odour Shield at £25 to £35 per metre.
- Butyl bends easily. Routing it through tight bulkheads takes far less effort than wrestling with rigid PVC.
- Fit two 316-grade stainless steel Jubilee clips at every connection. Tighten them to a torque of 4Nm.
- Warm the hose ends gently with a heat gun before pushing them onto the tailpieces.
- Never use grease or washing-up liquid to force hoses on. The pipe will slip off under pressure.
Unblocking the Holding Tank Vent
Holding tanks need oxygen to encourage aerobic bacteria. These organisms break down waste without producing foul smells. Starve the tank of air and anaerobic bacteria take over. They produce toxic hydrogen sulphide gas. This gas is deadly in high concentrations. Ensure good ventilation when working near an open holding tank. Check your tank vent line. This is usually a 16mm or 19mm (5/8 or 3/4 inch) hose running from the top of the tank to a hull skin fitting. Spiders, salt crystals and overfilled waste block this vent. Replace inline activated carbon filters annually. A carbon filter gets ruined the moment an overfilled tank wets it. It then blocks the airflow completely.