Portable Toilets on Boats: Emptying, Chemicals, Odor, Seals and Winter Storage

Read the manual for your model. Fill the fresh-water tank and add the flush-water additive if your maker recommends one. Add the holding-tank additive to the waste tank, with the small amount of water the label calls for, so the bottom of the tank is covered. Thetford says its waste-tank additive controls odor, reduces gas buildup and breaks down waste for easier emptying.

A loose toilet slides and tips in a wake. Use the maker's hold-down kit or floor plate (Thetford sells both and says the toilet can still be released quickly for emptying), or strap it into a cabinet or a locker built to fit. Put it where the user is stable and has a handhold, and where a spill won't run into the bilge.

• Open the valve, use the toilet, flush with a few pumps of water, then close the valve to keep odor in the tank.
• Use quick-dissolving paper made for RVs or boats. Wipes, paper towels, feminine products and trash go in a bag, never in the tank.
• Keep an eye on the level indicator if yours has one (Thetford's uses a float with a magnet) and empty it before it's full.

Thetford recommends emptying the waste tank every 4 to 5 days, depending on the additive you use. On a hot boat, more often is better: heat speeds up odor and gas. Don't let a partly full tank sit in a closed boat all week.

Look for a dump station (sometimes called a porta-potty dump or "portable toilet dump") at marinas and launch ramps; many are listed in state Clean Vessel Act maps and pump-out apps. Oregon Sea Grant notes that its state's dump stations take waste from portable toilets, buckets and similar containers, that many are free, and that some charge a small fee. Some areas also have floating restrooms. If there's no dump station, a regular flush toilet at home or an RV dump can usually take it; check that the facility allows it. The pump-out station guide explains how marina stations work.

1. Close the valve and unlatch the waste tank from the top section.
2. Carry it upright to the dump station.
3. Turn the spout toward the opening and remove its cap.
4. Pour slowly with the spout low. If your model has a vent button on the spout, press it only once the spout points down; it lets air in so the tank empties without splashing (check your manual).
5. Rinse the tank with a little fresh water, swish and pour again until it runs clear.
6. Cap the spout and add fresh additive before reattaching.

Oregon Sea Grant asks boaters to keep trash, including personal wipes, out of dump stations and put it in a garbage can instead. Rinse the station's sink if there's a hose for it.

Use additives made for portable toilets and dose them as the label says; household cleaners aren't designed for this, Thetford warns. NC Wildlife points out that deodorizers containing formaldehyde, chlorine and ammonium compounds are harmful in the water, which is one more reason never to dump a tank illegally. Some marinas and septic-based dump stations ask for biodegradable, formaldehyde-free products; check local rules and use those where required. Never mix different chemicals in the same tank.

If it smells:

• Empty and rinse it more often, especially in hot weather.
• Make sure the valve is fully closed after each use.
• Check the dose of additive; too little is common.
• Clean under the rim and around the valve with a toilet-only brush.
• Check the seals (step 9). A tired valve seal lets odor escape.
• Ventilate the cabin; the mold and mildew guide helps with general boat odor.

The sliding valve and its rubber seals keep odor in and prevent leaks. Thetford recommends its seal lubricant to keep seals soft. Use only the maker's lubricant or one it approves; don't use petroleum jelly or cooking oil, which can damage rubber. If the valve sticks, leaks or the tank smells even when closed, clean the valve area and lubricate it; replace worn seals or parts with the ones for your model.

Thetford advises cleaning the waste tank with its tank cleaner 2 to 3 times a year to remove scale and deposits. Rinse well afterward. Clean the bowl with a mild cleaner approved for the toilet; harsh household products can damage seals and plastic.

Thetford lists its Porta Potti models as working between about 34°F (+1°C) and 140°F (+60°C), and safe in storage down to about -40°F (-40°C). The catch is water: anything left inside can freeze and crack tanks, the pump or the valve. Don't leave it in direct sun in a closed, hot cabin either.

1. Empty, rinse and clean the waste tank at a dump station.
2. Empty the fresh-water tank and pump the flush pump until no more water comes out.
3. Let both sections dry fully with the caps off.
4. Lubricate the seals as your maker suggests.
5. Store it indoors, somewhere dry. Many manuals say to leave the valve slightly open during storage so the seal doesn't stick, and to loosen the fill cap so the tank can breathe; follow yours.
6. If it has an electric flush pump, take out the batteries.

In spring, check the seals, refill, add chemicals and test it at home before the first trip.