How to Winterize Your RV or Boat Toilet (and the Parts That Crack When You Don't)

If your RV or boat is going into storage for the winter, the toilet needs to be winterized along with the rest of the plumbing. It takes about 20 minutes. Skip it, and come spring you may find a toilet that won't stop running or is leaking onto the floor.

As the Dometic Master Sanitation Distributor for the Western United States, we ship Dometic and SeaLand toilet parts to RV and boat owners every day. Since Dometic acquired SeaLand, both names appear on the same toilets and parts, so you'll see us use them together. Here's how to winterize a Dometic/SeaLand toilet the way the manufacturer recommends, and which parts to check before you put it away.

Why freezing damages RV and marine toilets

Water left in the toilet's water valve or supply line expands as it freezes. That pressure can crack the valve, even when the rest of the plumbing was blown out. You usually won't see the damage until you turn the water back on.

On Dometic 310 and 320 series toilets, the water valve has a small freeze-damage indicator window. White stress marks in that window mean the valve has frozen. Dometic's warranty for these toilets does not cover freeze damage from improper winterization, so a cracked valve is an out-of-pocket repair.

The good news: the fix for a damaged valve is a bolt-on replacement kit, and the prevention is simple.

How to winterize a Dometic/SeaLand toilet: clean, drain, protect

Dometic recommends one of two methods: drain the system completely, or fill it with potable-water antifreeze. Many owners do both. Always check your toilet's owner manual for model-specific steps.

Step 1: Clean the system

1. Fill the bowl with water and add about 4 oz of biodegradable, bleach-free liquid laundry detergent.
2. Flush continuously for about two minutes to clear the bowl, hoses and pump.
3. Rinse with fresh water and brush away any loosened deposits.

Step 2: Drain the toilet and lines

1. Flush the system thoroughly with fresh water.
2. Empty the holding tank.
3. Shut off the water supply to the toilet.
4. Disconnect the inlet water line from the toilet's water valve. Do not remove the brass cap on the bottom of the valve.
5. Press the flush pedal or lever until all water has drained out of the toilet and valve.
6. Drain the discharge hoses and holding tank so odors don't build up over the winter.

Step 3: Protect with antifreeze (optional, but good insurance)

1. Drain the potable (fresh) water tank.
2. Add nontoxic antifreeze rated for potable water systems to the tank.
3. Flush the antifreeze mixture through the toilet and into the holding tank. The amount varies by installation.
4. Empty the holding tank.

Never use automotive antifreeze in a fresh water or toilet system. Use only the pink, potable-water-safe RV and marine antifreeze.

Jabsco and Raritan marine heads have their own procedures, especially manual and macerating models. Follow the owner's manual for your model, and see the parts list below for the seals and valves to check.

Parts to check before you store your RV or boat

Fall is the best time to replace worn parts. You'll find problems while the toilet is already apart, and you won't be waiting on shipping when you want to use it in spring.

Not sure which part fits your toilet? Find your model on our VacuFlush and MasterFlush diagram pages, or browse all service kits.

Winterizing FAQ

Do I need antifreeze to winterize my RV toilet? Not always. Dometic says you can winterize by draining the system completely or by using potable-water antifreeze. Antifreeze adds protection if any water is left in the valve or lines.

What kind of antifreeze is safe for an RV or marine toilet? Only nontoxic antifreeze made for potable water systems. Never use automotive antifreeze.

Why is my RV toilet leaking after winter? A common cause is a water valve that cracked when trapped water froze. On Dometic 310 and 320 toilets, white stress marks in the valve's indicator window confirm freeze damage. Replacing the water valve kit usually fixes it.

Does Dometic's warranty cover a frozen water valve? No. Dometic's warranty excludes damage from improper winterization, including a freeze-damaged water valve.

How do I winterize a VacuFlush toilet? Clean it with bleach-free detergent, drain the toilet, discharge hoses and holding tank, then optionally flush potable antifreeze through the system. On pedal-operated VacuFlush toilets, remove the supply line from the water valve so the valve drains.

Should I replace parts before or after winter storage? Before. Fall is the best time to replace worn seals, valves and service kits, so the toilet is ready when you take the RV or boat out in spring.

Get the right parts before storage season

Winterizing takes an afternoon. Replacing a cracked valve in spring takes a part you may have to wait for. Order genuine Dometic/SeaLand parts now from the Dometic Master Sanitation Distributor for the Western United States, shipped from our Wilmington, CA warehouse. Parts orders over $100 ship free.

Need help finding the right part? Ask James! Text or call (562) 387-6602.

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