Marine Head and Holding Tank Care: Odors, Clogs, Pump-Outs and Winterizing

Most clogs come from what goes into the bowl. Only human waste and a modest amount of quick-dissolving toilet paper (or no paper: many owners keep a lidded trash bin in the head). Never flush wipes (even "flushable" ones), paper towels, feminine products, hair or food. Post a short note in the head for guests.

Know your tank's size and how many flushes it takes to fill. Pump out often. An overfilled tank pushes waste up the vent line and into the pump-out hose, causing clogs and smells. If you have a tank level gauge, test it now and then; they are often unreliable.

Wear gloves. Open the deck fitting marked WASTE (never confuse it with fuel or water fittings). Read the pump-out station's instructions. With the station pump running and the nozzle valve closed, seat the nozzle firmly in the deck fitting, then open the valve. When the flow stops (a sight glass or sound tells you), let the pump keep running a moment to clear the hose, close the valve, and remove the nozzle. Then flush some fresh water through the head into the tank and pump out again. Close the deck cap tightly.

Saltwater flushing leaves scale in the pump, valves and discharge hose, which slowly makes pumping harder and lets water seep back into the bowl. Once a month, run about a pint of white vinegar through the head slowly (one pump every few minutes), then flush with fresh water. Keep the pump seals supple with the lubricant your toilet maker specifies (Raritan, for example, recommends a PTFE silicone grease on the pump). Skip the old habit of pouring vegetable or mineral oil into the bowl: it only quiets a squeak for a while, and Practical Sailor's long-term test linked it to clumping in the holding tank. Avoid harsh household cleaners and bleach, which can damage rubber parts and kill the helpful bacteria in the tank.

Work through the usual suspects:

• Discharge hose permeation: wipe a section of hose (a low spot where waste sits is best) with a warm, damp, clean cloth. BoatUS suggests sealing the cloth in a zip-top bag, carrying it up into fresh air, then opening the bag and sniffing; inside the boat your nose is already used to the smell. If it smells, the hose is saturated and must be replaced with proper sanitation hose, including the tank vent hose. Washing will not fix it.
• Intake smell (rotten-egg whiff when you flush): about a gallon of seawater sits in the intake hose, and when the boat isn't used for a few days the tiny sea life in it dies and rots. SAIL notes it clears with the first flush, and a splash of holding tank deodorant in that first flush helps. A strainer in the intake helps too. Flushing with fresh water before leaving the boat, or leaving vinegar in the lines, also helps.
• Vent line: a blocked vent makes the tank smell worse (it needs air). Mud daubers and other insects love to nest in the vent fitting, and an overfilled tank pushes sewage into the vent hose. BoatUS adds that a clogged vent can let the tank collapse under the suction of a pump-out. Back-flush the vent when you pump out if you can. A vent filter reduces smell outside the boat, but filters lose their effect over time and need replacing as the maker says.
• Hose runs with low spots: hoses should be as short and straight as possible, with no loops or sags where waste can sit. The pump-out hose from the deck fitting should drain back into the tank.
• A shower that drains into the bilge, or a dead shower sump: both cause smells that seem to come from the head. Clean the sump strainer and test its pump and float switch at least once a year.
• Leaks: look at every hose joint, clamp and the toilet base for drips or stains.

Stop pumping first; forcing it can split a hose or valve. Then narrow it down:

• Check the Y-valve is fully in one position. A half-turned valve blocks flow.
• Hard to pump and bowl won't empty: the blockage is usually at the joker valve (the rubber duckbill valve at the pump outlet) or in the first section of discharge hose, often from scale or something that should not have been flushed.
• Pumps fine but water comes back: worn joker valve or flapper valves.

With seacocks closed and gloves on, remove the discharge hose at the toilet and look inside. Scale can be broken out of a removed hose by flexing it or tapping it; heavily scaled hose is usually best replaced. Never use household drain cleaners; they can damage the toilet and are dangerous with sewage.

If the toilet is hard to pump, leaks back, or smells even when clean, it is probably time for a rebuild kit for your model. The kit includes valves, seals and instructions. BoatUS tips: take the toilet out of the head compartment to work on it, lay the parts out in order, and note which way each valve faces. Tighten the bowl-to-base nuts evenly and gently to avoid cracking the china.

• Station runs but nothing comes out: the pump-out hose may be clogged (often from overfilling) or the vent may be blocked. Check the vent fitting on the hull first; the small screen often clogs with salt, insects or corrosion. A plastic snake can clear the vent hose.
• Tank fills even when nobody uses the head: often an open overboard (macerator) seacock or Y-valve lets seawater flow back in. Close and secure it.

Regular pump-outs leave some buildup behind. A common approach is to pump out, add a water-softener solution and a mild, bleach-free laundry detergent solution made with hot water, let it sit, top up with fresh water, pump out, then rinse and pump out again. A tank treatment made for holding tanks also works. Only use products compatible with your tank material (plastic, aluminum or stainless), and never mix different chemical products. BoatUS suggests a shock treatment at least once a year, and adding one about a week before the last pump-out of the season while you still use the boat, so it sloshes around and the tank goes into winter clean.

Squeeze the sanitation hoses: gummy, hard or cracked hose should be replaced. Check clamps for rust, and make sure hoses below the waterline are double-clamped where possible. Work the head's seacocks open and closed; they should move freely. See the seacocks guide for more.

Before freezing weather:

1. Pump out the tank and flush it with fresh water, then pump out again.
2. With the intake seacock closed, pump non-toxic propylene glycol (pink) antifreeze through the head until it comes out pink into the tank. Follow the antifreeze label for freeze protection.
3. If you have a macerator, run a little antifreeze through it briefly (as its maker allows) and close its seacock.
4. Leave some antifreeze in the tank only if the product and your marina allow it, and drain or protect any freshwater flush lines as part of your freshwater system.
5. Close all head seacocks and tag them.

Never use automotive (ethylene glycol) antifreeze in the head or water system.

Open the seacocks, pump fresh water through and check every hose and joint for leaks. Lubricate the pump. Record the date of rebuilds, hose changes and pump-outs in BoatMend.