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There’s not a lot that’s worse than finding your RV toilet leaking (except maybe finding your black tank leaking!), but it helps to know what’s causing the leak so that it can be repaired as quickly as possible.

In today’s post, we’re going to run through the various reasons why an RV toilet might be leaking, and what you can do to troubleshoot your leak, and repair it.

What Would Cause an RV Toilet to Leak?

The first thing to do when you find a leak that appears to be coming from your toilet is to investigate the area to find out exactly where the leak is coming from and when it’s happening.

For example, is the water dripping from the upper part of the toilet when you flush it? Is the leak happening when the toilet bowl is full? Are you finding water around the base of the toilet?

Once you’ve determined the origin of the leak, you’ll be able to spring into action to repair it.

RV toilets usually leak for one of these reasons:

Bad Flange Seal

This is the seal between the toilet and the floor (like the wax seal under your home toilet). From time to time, these seals can come loose or develop gaps that cause leaking.

Here’s an example of a Dometic flange seal followed by a standard (supposedly universal) 3” flange seal:

DOMETIC 385311267 Floor Flange Seal Kit
  • Floor flange fits 110 and 210 Series Domestic RV toilets
  • Seals to prevent leaks
Thetford 33239 Closet Flange Seal , Gray
  • Closet flange for Thetford toilets
  • Replaces 02125

Cracked Water Valve

A cracked water valve could allow water to continue flowing into your toilet bowl, eventually causing it to overflow. To see a water valve being replaced in a Dometic RV toilet, check out this video from RV Living Yet.

This is a Dometic Sealand water valve kit:

Sale
DOMETIC 385311641 Sealand Water Valve Kit , white
  • Includes water valve, hose clamp, fasteners and instructions
  • Package Dimensions: 12.7 L x 2.54 H x 10.414 W (centimeters)

Bad Valve Seal/Flush Ball Seal

The “valve seal” or “flush ball seal” is the seal inside the toilet bowl that holds water (and the other contents) until you flush… AND keeps odors from the black tank below from coming up into the livinst area of your RV.

DOMETIC (385311658 Flush Ball Seal Kit
  • Includes seal and instructions only
  • Package Dimensions: 0.254 L x 16.764 H x 14.224 W (centimeters)

Cracked Bowl

This is more likely to happen with an RV toilet that has a plastic bowl. A small crack may have developed that allows water to drain out of the bowl during use.

Dometic 302320081 320 Series Standard Height RV Toilet, White
  • Deep, 100% Vitreous Ceramic Bowl | Full-Size Residential Style Wood Seat
  • Dimensions – 22” L x 14.75” W x 19.75” H | Weight – 36.99 lbs. | From the center line of the bolts to the back of the base at the bottom...

Loose or Cracked Fittings

Here you would need new fittings or you may only need to re-wrap the current fitting/fittings with new Teflon tape and tighten the fitting.

What is the Most Common Reason for an RV Toilet to Leak?

The most common reason for an RV toilet to leak is a bad flange seal.

The flange seal is the rubber ring that seals your RV toilet to the floor. Also called a closet flange seal, this seal is similar to the wax seal under your home toilet. Over time, movement from driving and flexing from the weight on the bowl can cause this seal to fail.

Your first step, though, is to confirm that the bolts holding the toilet to the floor are secure. Your “leaking flange seal” may actually be caused by loose bolts. If that doesn’t solve the problem, and your issue is that your toilet leaks at the base when you flush, you’ve likely got a bad flange seal. Let’s take a look at how to replace it, DIY style.

How Do I Replace the Flange Seal on my RV Toilet?

You’ll need the following items:

  • Replacement flange seal – this one fits a standard 3” ring:
Thetford 33239 Closet Flange Seal , Gray
  • Closet flange for Thetford toilets
  • Replaces 02125
  • Socket set or wrench
  • Towels
  • Putty knife or utility knife to remove the old flange seal
  • Teflon tape
  • Rubber gloves
  • Cleaning supplies

Replace the old flange seal by taking the following steps:

  1. Shut off the water supply to the toilet (and/or RV) and be sure the water pump is turned off
  2. Disconnect the toilet from the water supply (locate the water pipe and unscrew it, freeing the water pipe from the toilet… it’s likely hidden up behind the toilet)
  3. Locate the bolts holding the toilet to the floor and remove them. Pull the toilet straight up off the floor.
  4. Locate the old flange seal. (Note: It may be stuck to the bottom of the toilet.) Remove the old flange seal and cover the sewer hole with an old rag or plastic bag (to prevent odor).
  5. Clean the bottom of the toilet bowl and the floor around the sewer ring very well.
  6. Install the new toilet flange seal.
  7. Remove the bag or rag from the sewer hole and lift the toilet carefully onto the flange seal, being careful to place the toilet in line with the bolts.
  8. Using your wrench, replace and tighten all of the bolts that hold the toilet to the floor.
  9. Reconnect the water, and test for leaks by flushing the toilet a few times.

What’s Wrong With My RV Toilet? Water Doesn’t Stay in the Toilet Bowl?

If water doesn’t stay in the bowl between flushes, then you’ve got a bad valve seal (also referred to as a flush ball seal). This is the black seal that you can see by looking into the toilet. Its purpose is to seal the blade valve that holds water in the bowl and opens to allow the contents of the bowl to flow into the black tank.

These seals can dry out over time and can crack and cause gradual leaking of the water out of the toilet bowl (and/or odors from the black tank back into the bathroom). To prevent this from happening you can occasionally treat the seal with a conditioner/lubricant to keep the valve sea operating smoothly and prevent it from drying out.

Thetford RV Toilet Seal Lube and Conditioner - Toilet Seal Lubricant - 24 oz 36663
  • [VERSATILITY]: Thetford's RV Toilet Seal Lube & Conditioner works with all permanent or portable toilets found in RVs and boats
  • [FUNCTIONALITY]: Penetrates the toilet seal, lubricating and protecting

This is an example of a valve seal/flush ball seal, but this one may not fit your RV toilet. Again, you’ll need to check the make and model of your RV toilet, and then order the appropriate seal to fit.

DOMETIC (385311658 Flush Ball Seal Kit
  • Includes seal and instructions only
  • Package Dimensions: 0.254 L x 16.764 H x 14.224 W (centimeters)

How Do I Change the Valve Seal/Flush Ball Seal of my RV Toilet?

The typical process for replacing the flush ball seal would involve dismantling the toilet to get to the valve. You’ll want to refer to your RV toilet’s owner’s manual for the exact procedure for your make & model. Here’s an example of our friend Brian at RVwithTito.com replacing the valve seal on his Thetford toilet:

However, some RV toilets, specifically the newer Dometic toilets, allow you to replace the flush ball seal from above without dismantling the toilet, making it a much easier repair.

Why Would an RV Toilet Leak from the Top?

If the toilet is leaking from the top portion during the flush cycle, then you may have a bad float seal in the vacuum breaker. In this case, you may be able to buy a kit to replace the float seal or take the current float seal mechanism apart to be thoroughly cleaned.

Let’s take a look…

How Do I Know If My RV Toilet Vacuum Breaker is Leaking?

Your RV toilet’s vacuum breaker can leak due to age or wear & tear. If water is leaking from the upper part of the toilet, and especially if the back of the toilet is wet, the problem may be the toilet’s vacuum breaker.

Note: the float seal can also leak from the same area, so you need to determine whether the leak is caused by the float seal or the vacuum breaker. To do this, look inside the toilet bowl. If the problem is the float seal, it’s likely to appear cracked, dried out, or damaged in some way. If the float seal looks good, your vacuum breaker is the likely culprit of water leaking from the upper part of the toilet.

How to Repair a Leaking RV Toilet Vacuum Breaker

  1. Locate your RV toilet’s model / serial number near the bottom of the toilet. There are parts that are universal, but having your toilet’s make and model number will allow you to make sure the parts will fit your toilet before ordering.
  2. Shut off the water supply to the toilet (but have a towel on hand for any excess water).
  3. Locate the hose that connects the toilet to the supply line near the foot pedal valve, and loosen the hose clamps.
  4. Slide the hose off and pull out the vacuum breaker.
  5. Identify the rubber grommet holding the vacuum breaker to the toilet and remove the grommet with your finger. (Stick a finger into the rubber grommet and pull it out.)
  6. Clean the area well.
  7. Install the new rubber grommet and insert the new breaker.
  8. Reattach the hoses (new hoses may come with your kit), and turn the water supply back on.
  9. Test for leaks by flushing the toilet.

What If My RV Toilet Leaks When the Bowl is Full of Water

This may be an indication of a cracked toilet bowl, especially if you have a plastic toilet as this is more common with plastic toilets than with porcelain bowls.

Check the connections behind the toilet and make sure the leak is not coming from these connections.

If you determine that the toilet bowl is cracked, you’ll need to replace the entire toilet (and maybe you’d like to consider replacing your standard RV toilet with a composting toilet instead?).

For More Information…

For more information on RV toilets in general, feel free to check out our post and video entitled “RV Toilet Talk: How Does an RV Toilet Work?”, and we’ll help you to flush out the details! (Sorry – we couldn’t help ourselves!)

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Sometimes we receive products for evaluation at no cost and may use affiliate links to the products and services from which we earn commissions. For example, as an Amazon Associate, we earn from qualifying purchases. That said, it's important to us to let you know that our opinions are our own. We only recommend products we believe deliver real value and that we can confidently recommend without reservation. You also won’t pay an extra penny by using our links. Thanks so much for supporting RVgeeks as we work to create helpful RVing-related content that we hope enhances your RVing life!

Even though we're handy RVers, we're not professional technicians. So although we're happy with the techniques and products we use, you should be sure to confirm that all methods and materials are compatible with your equipment and abilities. Regardless of what we recommend, consult a professional if you're unsure about working on your RV. Any task you perform or product you purchase based on any information we provide is strictly at your own risk.

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