RV Toilet Seal Replacement - Stop Leaks and Odors

A worn toilet seal lets sewer gas into your camper. You’ll smell it before you see it. The seal also keeps water in the bowl — when it fails, the bowl drains and there’s nothing between you and the black tank below.

Replacing it takes 30 minutes and a $15 part.

Symptoms of a Bad Seal

• Sewer smell in the bathroom even with the flush pedal up
• Bowl won’t hold water — it slowly drains after flushing
• Water around the toilet base when flushing
• Visible wear or cracking on the seal when you look inside the bowl

Identify Your Toilet

Check the brand name stamped on the toilet. The two main RV toilet manufacturers:

Thetford — Aqua Magic series. Uses a ball valve with a round rubber seal.

Dometic — 300/310/320 series. Uses a blade valve with a flat rubber seal.

The model number is usually on a sticker behind the toilet or inside the bowl rim. You need this to order the right seal kit.

Parts and Tools

Parts

• Replacement seal kit (specific to your toilet model)
• New flange bolts and gasket (if the base seal is leaking)
• Plumber’s grease or silicone lubricant

Tools

• Phillips and flathead screwdrivers
• Adjustable wrench or socket set
• Towels and a small bucket
• Rubber gloves

Replacing a Thetford Ball Seal

1. Prep

Turn off the water supply to the toilet. Flush to empty the bowl. Put towels around the base.

2. Access the Seal

The ball seal is visible inside the bowl at the bottom. On most Thetford models, you can access it without removing the toilet.

Press the flush pedal to rotate the ball. Look for cracks, flat spots or hardened rubber on the seal ring.

3. Remove the Old Seal

Pop out the retaining ring (if equipped) with a flathead screwdriver. Pull the old seal off the ball. Clean any residue from the ball surface.

4. Install the New Seal

Apply a thin coat of plumber’s grease to the new seal. Slide it onto the ball in the same orientation as the old one. Snap the retaining ring back in place.

5. Test

Turn the water back on. Fill the bowl. Let it sit for 10 minutes. If the water level holds, the seal is good. Flush a few times to make sure it seats properly.

Replacing a Dometic Blade Seal

1. Prep

Same as above — water off, bowl empty, towels ready.

2. Remove the Toilet (Usually Needed)

Dometic blade seals typically require removing the toilet from the floor for full access.

Remove the two flange bolts at the base. Disconnect the water supply line. Lift the toilet straight up and set it on towels.

3. Access the Blade

With the toilet removed, you can see the blade mechanism from below. The seal sits on the blade edge.

4. Swap the Seal

Remove the old seal from the blade. Clean the blade edge. Apply plumber’s grease and press the new seal into position.

5. Reinstall

Set the toilet back on the flange with a new wax-free gasket. Tighten the flange bolts evenly (alternate sides). Reconnect the water line. Test for leaks.

Extending Seal Life

• Keep water in the bowl at all times. A dry seal dries out and cracks.
• Use RV toilet chemicals that are seal-safe. Avoid harsh cleaners with bleach or petroleum solvents.
• Lubricate annually. Apply plumber’s grease or a product like Thetford Toilet Seal Lube to keep the rubber supple.
• Don’t force the flush pedal. Excessive pressure wears the seal against the ball or blade.

When to Replace the Whole Toilet

If the toilet is over 10 years old, the porcelain or plastic is cracked, or the flush mechanism is worn beyond seal replacement, a new RV toilet costs $80-300. Installation is the same process as removing and reinstalling for a seal change.

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