The Marine Head: Only the 3 P's

A marine head is a boat's toilet, and it's the system most likely to fail embarrassingly for one reason: nothing goes into it except the three P's — pee, poo, and (marine-safe) paper. Everything else — wipes, tampons, paper towels, cotton buds, cooking grease — jams the narrow pump valves and hoses. Unlike the wide, forgiving plumbing at home, a head's discharge line can be as narrow as 1 inch, so a single wad of the wrong paper can clog it.

Waste doesn't vanish; on most cruising boats it's pumped into an onboard holding tank. Operating a manual head correctly means using enough water to carry waste through: pump on the 'wet' setting to flush it into the tank, then switch to 'dry' and pump several more strokes to push the waste all the way along the hose so nothing sits and dries into a blockage. Too little water is the classic cause of a clog.

Where that waste can legally go is strictly controlled. In many coastal and inland zones — including designated No-Discharge Zones and all US inland waters — you may not discharge sewage overboard at all, even if treated. You must hold it and empty the tank at a shoreside pump-out station. Discharging raw sewage is typically only permitted well offshore (commonly beyond 3 nautical miles in US waters), so plan pump-outs before they're urgent.

A practical habit: brief every guest on the three P's before they use the head, keep a Y-valve (if fitted) set to the holding tank in restricted waters, and never assume 'it'll flush' — the sea has no plumber.