RV Toilet Seal Replacement: Bowl, Waste Ball and Floor Seals by Model

You wake up in the middle of the night, walk into your RV bathroom, and immediately know something is wrong. The toilet bowl is completely dry. Worse, there’s a faint sewer smell hanging in the air.

You didn’t leave the black tank valve open. Nothing is clogged. The problem is simpler: your RV toilet seal has failed.

RV toilet seal replacement is a repair many owners handle themselves. How long it takes depends on which seal has gone bad: the Dometic flush ball seal is replaced from inside the bowl, while a floor seal means lifting the toilet off the floor. The tricky part is knowing which seal is causing the problem and which steps apply to your specific toilet brand.

This guide covers both Dometic and Thetford toilets. It walks you through how to diagnose the problem, get the right replacement part, and fix the flush ball seal, waste ball seal, and floor flange seal correctly. It covers the rubber and foam seals only. If the rigid plastic floor flange itself is cracked or loose, use our RV toilet flange replacement guide instead.

Which RV Toilet Seal Needs Replacing?

Quick Answer: Most RV owners deal with two seals: the bowl seal (the flush ball seal on Dometic, the waste ball seal on Thetford), which holds water in the bowl, and the floor flange seal, which stops leaks at the toilet base. Water valve and vacuum breaker leaks can look similar, but they are valve problems, not seal problems. Match your symptom to the right part before ordering anything.

A dry bowl also lets black tank gases into your living space. That sewer smell in the morning is the seal telling you it’s done. For more help diagnosing odors that persist even after a seal replacement, check out our guide on RV toilet smells when flushed.

Should You Replace the Seal or Clean It First?

Not every bowl water problem means the seal is worn out. Before ordering a replacement, take 10 minutes to clean the bowl and flush seal gently and recondition the existing seal as your manufacturer directs. Dometic’s own installation instructions note that a bowl not holding water can result from a seal that is incorrectly positioned, temporarily distorted, dirty, or worn. Only the last one requires a new part. If you’re still working out why the bowl won’t hold water, our RV toilet bowl not holding water guide covers the other causes.

Clean and recondition first if:

• The seal looks intact but has a visible coat of mineral deposits or residue
• The bowl started losing water after a long storage period (dry-out, not damage)
• The seal still feels pliable when you press it, not hard or cracked

Replace the seal if:

• The rubber is visibly cracked, torn, swollen, or misshapen
• The seal feels hard and won’t compress evenly around the flush ball
• The bowl still won’t hold water for 30 to 60 minutes after cleaning and lubricating
• The seal has a visible gap or doesn’t seat flat all the way around

How to clean the seal before replacing:

1. Open the flush ball (Dometic) or remove the bowl (Thetford) to access the seal.
2. Put on rubber gloves and remove the seal.
3. Soak a cloth in white vinegar and scrub the seal and the seal seat to remove mineral buildup.
4. Rinse clean and let dry.
5. Apply the lubricant your toilet’s maker specifies. Thetford’s owner manual says not to use petroleum-based products on its toilets; Dometic’s instructions differ, so check them first.
6. Reinstall and test. Fill the bowl and check at 30 minutes and again at 60 minutes.

If the bowl still drains after cleaning and reconditioning, the seal is worn. Order the replacement part and follow the steps below.

Which Seal Fits Your Toilet? Seal Part Numbers by Model

Quick Answer: On Dometic 400-series toilets, Dometic lists the flush ball seal kit as 385311658, and retailers list the same kit for the 300, 310, and 320. On Thetford Aqua-Magic toilets the waste ball seal depends on the model: 34120 for Style Plus and Style Lite, 42141 for Style II and Residence on Thetford’s current parts lists, and blade seal 31708 for the Aqua-Magic V. Thetford lists closet flange seal 33239 for all of these models. Always confirm against the model label on your toilet.

For more Thetford part numbers by model, see our Thetford camper toilet parts guide, and for Dometic and other brands, our RV toilet parts guide.

Parts and Tools to Get Before You Start

Ordering the right part for your specific toilet model matters. Seal kits are model-specific, and Thetford part numbers vary by model line, as the table above shows. Check the model sticker on your toilet before you order anything. It’s usually on the back wall of the bowl or under the foot pedal housing. If you’re weighing a cheaper seal, compare OEM and aftermarket RV toilet seals first.

For Dometic gravity-flush toilets (300, 310, and 320 series; retailers also list many 400-series models as compatible):

• Flush ball seal: Part #385311658, the rubber gasket inside the bowl.
• Floor seal kit: Part #385311652, retailer-listed as the base seal for the 300 series. Some retailers describe this number as a mounting hardware kit, so confirm with Dometic’s parts list before ordering.
• Water inlet valve: Part #385311641, if flushing causes a drip from the back of the toilet.

For Thetford Aqua-Magic Style Plus and Style Lite:

• Waste ball seal kit: Part #34120, the rubber seal around the waste ball inside the bowl.
• Style II and Residence: Thetford’s current parts lists give waste ball seal 42141. Aqua-Magic V uses blade seal 31708. Other models use model-specific parts, so check the label on your toilet before ordering.

Check part numbers before you order. Dometic’s installation and operating manual names the flush ball seal kit, the water valve kit, and the floor flange seal, but prints a part number only for the water valve kit and points you to Dometic’s online parts list for the rest. Retailers list more than one number for the same Dometic seal kit. Confirm the number against your toilet’s model and serial label, or with Dometic, before ordering. Thetford’s Style II waste ball seal kit instructions reference part number 34120, while Thetford’s current Style II parts list gives waste ball seal 42141. Check your toilet’s label before ordering.

Tools:

⚠️ Safety check before you start: Turn off the water supply and fully release pressure before touching any toilet component. If removing the toilet from the floor, dump and rinse the black tank first. Wear rubber gloves throughout. Have old towels nearby for water spillage.

• Adjustable wrench
• Pliers
• Rubber gloves
• Old towels or rags
• Silicone-based plumber’s grease

One critical note on lubricant: follow the instructions for your exact toilet. Thetford’s permanent toilet owner manual says not to use petroleum-based products; Dometic’s 300/310/320 instructions allow a thin film of silicone grease or petroleum jelly when installing a new flush-ball seal. See our RV toilet seal lubricant compatibility guide before applying any product.

How Do You Replace the Flush Ball Seal on a Dometic RV Toilet?

The Dometic flush ball seal (part #385311658 at most retailers) is replaced from inside the bowl. Turn off the water, open the flush ball, pull out the old seal, press the new one in, apply silicone grease, and test. No toilet removal is needed. Dometic’s manual says to follow the detailed instructions packed with the seal kit, so read those before you start.

The Dometic 300, 310, and 320 series toilets use a rubber seal inside the bowl that wraps around the flush ball opening. When that seal dries out or tears, the bowl slowly drains. Unique Camping + Marine’s repair guide for the Dometic 300 series walks through the job from inside the bowl and calls it a simple and easy process.

Step 1: Turn off the water supply. Shut off the pump at the control panel or disconnect from city water.

Step 2: Press the foot pedal all the way down to open the flush ball. Hold it open and let any remaining water drain into the black tank.

Step 3: With the flush ball open, reach in with gloved hands and pull the old seal straight down and out of the flush valve opening. It should release without tools.

Step 4: Clean the flush valve opening. Remove any mineral buildup or debris left behind by the old seal.

Step 5: Press the new seal into the flush valve opening. Push firmly all the way around to make sure it’s fully seated.

Step 6: Apply a thin coat of silicone grease to the surface of the flush ball where it contacts the seal.

Step 7: Close the flush ball. Turn the water back on. Add water to the bowl and leave it for at least 30 minutes to confirm the seal holds.

If your Dometic is leaking at the base rather than draining through the bowl, that’s a separate issue. Our full guide on Dometic RV toilet leaking at the base covers every cause and the correct fix for each.

How Do You Replace the Waste Ball Seal on a Thetford RV Toilet?

Thetford’s instructions for the Aqua-Magic Style II waste ball seal kit (part 34120 on that kit sheet) have you remove the toilet from the floor first, then lift the bowl off the pedestal to reach the seal. Once the bowl is off, the old seal pulls out and the new one presses into place.

Thetford Aqua-Magic toilets take more work than Dometic models. Thetford’s instruction sheet for the 34120 kit starts with shutting off the water, lifting the toilet off the floor, and covering the holding tank opening, then removing the bowl-to-base screws and lifting the bowl off. It also recommends rinsing the toilet and draining the holding tank first to reduce odor. The steps below follow a common owner shortcut of lifting the bowl with the toilet still on the floor. If anything resists, follow Thetford’s sheet and remove the toilet first.

How Do You Replace the RV Toilet Floor Seal?

Quick Answer: Replacing the RV toilet floor seal means removing the toilet completely from the floor. Use the floor flange seal your toilet’s maker specifies, not a residential wax ring: Dometic’s 310 manual lists its floor flange seal as nitrile rubber and foam, and Thetford lists a dedicated closet flange seal (33239) for its Aqua-Magic models.

While the toilet is removed, inspect the floor flange for cracks, damaged mounting slots, or movement. If the flange itself needs work, follow our RV toilet flange replacement guide rather than treating it as a seal-only repair. If you are adding a height riser under the toilet, use the seals and hardware specified for that kit rather than assuming the existing floor gasket can be reused.

A base leak left unaddressed causes floor damage fast. This is one worth prioritizing.

Dometic’s manual says to remove and discard the old floor flange seal and hold-down bolts when you replace the seal, and some Dometic units arrive with the seal already fitted to the underside of the toilet. Follow the instructions that come with your seal or toilet.

One key distinction: if water only appears at the base during flushing and stops when the toilet is idle, the floor seal is probably fine. That specific pattern points to the water inlet valve instead. For Dometic toilets, see our Dometic RV toilet leaking at the base guide for how to tell the two problems apart.

How to Make Your New RV Toilet Seal Last Longer

Replacing the seal is step one. Making it last is step two. Dried-out rubber and mineral buildup are common reasons seals stop sealing, and a few habits help with both.

None of the Dometic or Thetford documents we checked publishes a seal lifespan. How long a seal lasts depends on water hardness, storage, cleaning habits, and how often the toilet is used, and regular care helps it last longer.

Lubricate the seal at the start and end of every season. Use the product your manual names: Thetford recommends its own toilet seal lubricant and conditioner, and Dometic’s instructions allow silicone grease. A thin coat helps keep the rubber supple.

Don’t let the bowl sit completely dry in storage. When the RV is parked for weeks or months, add a small amount of water or a few drops of RV toilet seal conditioner to the bowl. This prevents the seal from hardening while the rig is idle.

Release the foot pedal fully after every flush. Dometic’s manual says to release the pedal after a complete flush. Owners in a Forest River Forums thread report that letting the pedal close firmly, rather than easing it back, helps the bowl hold water. That is owner experience, not a manufacturer instruction.

Clean the seal periodically. Mineral deposits and toilet chemical buildup prevent the seal from sitting flush. A soft brush, white vinegar, and a rinse before applying fresh silicone grease will keep it clean.

Use only the lubricant your toilet’s maker allows. Thetford’s owner manual says not to use petroleum-based products on its toilets and recommends Thetford’s own seal lubricant and conditioner. Dometic’s 300/310/320 instructions allow a thin film of silicone grease or petroleum jelly when installing a new flush ball seal. Skip household oils and sprays the manual doesn’t name.

For more on keeping your whole RV sanitation system in good shape, see our guide on the best RV toilet treatment products for odor control and waste breakdown.

When an RV Toilet Leak Is Not a Seal Problem

Quick Answer: If water drips from the back of the toilet only while flushing, suspect the vacuum breaker or water valve, not a seal. Thetford’s Aqua-Magic manual says a vacuum breaker that leaks while flushing should be replaced, and a leak when you’re not flushing points to the water valve. Check these before buying any seal:

• Drip at the back while flushing: see our RV toilet vacuum breaker guide, and for Dometic toilets, our Dometic leaking at base guide, which separates valve leaks from seal leaks.
• Water at the base of a Thetford: our Thetford RV toilet leaking at base guide covers the floor seal and the other causes.
• Wet fitting or hose behind the toilet: that is usually the supply line; see our RV toilet water supply line leak guide.
• Cracked or loose floor flange: replace the flange itself with our flange replacement guide.
• Bowl drains even with a new seal: the flush ball itself may be scratched or not closing fully, often a pedal or linkage issue rather than the rubber.
• Cracked toilet base: no seal will fix it. Compare models in our best RV toilet replacement guide.

Frequently Asked Questions

Written by

RV Flush Guide Editorial Team

RV Flush Guide Editorial Team creates practical, research-based guides on RV toilets, plumbing, holding tanks, sewer systems, and sanitation. We use manufacturer documentation, product manuals, and reliable technical sources to make troubleshooting and maintenance easier for RV owners.