Saturday, December 9, 2023


Easy leaking toilet fix: Replace the ‘ball seal’ on your RV’s toilet

Welcome to “In the RV Shop with Dustin”. We recently had a customer in the shop with a toilet that was leaking water from the bowl into the holding tank. After performing a simple operation and visual inspection, we narrowed down the culprit to the “ball seal.” Did you know this replacement is so easy that just about anyone can do it?

Dometic Toilet bowl seal on a 310 model.

Here is a simple, step-by-step installation guide to help you with this repair

Dometic 300/310/320 Flush Ball Seal Installation


  1. Turn off water supply before working on the unit.
  2. Hold flush pedal down to keep flush ball open and to release the water pressure in system.
  3. Grasp inside edge of seal and pull upward to remove from toilet. Remember to use rubber gloves.
  4. Thoroughly clean lower bowl rim area where seal was located; you can even use an old toothbrush.
  5. Release flush pedal to close flush ball. Thoroughly clean surface of flush ball.
  6. Insert new seal in base, making sure seal is firmly pressed outward against lower bowl rim.
  7. Press flush pedal to open flush ball, and spread thin layer of silicone grease or petroleum jelly under the seal where it will contact flush ball. Release flush pedal.
  8. Lightly press down around circumference of seal to insure seal is in proper position.
  9. Turn on water supply.
  10. Add water to bowl and check for leaks.
Steps 1-4

Here is the Dometic Flush Ball Seal Replacement for 300 310 320 RV toilets. In addition, if you want to extend the life of your toilet bowel seal, I recommend that you use a toilet bowl lubricant and seal conditioner.

More from Dustin

Make sure you check out my website, California RV Specialists, and our YouTube channel for more helpful information, and see our published articles on and other social media pages.


Dustin Simpson
Dustin Simpson
With over 25 years in the RV Industry, Mr. Dustin Simpson has worn many hats. From an RV Technician, Warranty & Parts Administrator, Parts & Service Manager and Business Owner. Outside of these typical roles and responsibilities within the industry, Dustin enjoys being a Content Creator, Brand Ambassador, Author, and Expert Witness. He has served as an expert witness in multiple cases in California, Washington, Idaho, and Texas. His repair facility has been servicing customers at the same location since 2003. What sets us apart from the dealerships is we are here to fix and maintain what you have, and not sell you a new one. Whether you own a million-dollar unit or an entry level, my message to you will be the same, it needs to be maintained.


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L. B. (@guest_261322)
24 days ago

We just changed the seal on our Thetford toilet and the pedal still doesn’t fully close. We have to empty the tank every 2-3 days now, instead of every 5-6.

D Tipton (@guest_260916)
26 days ago

Great info. Unfortunately I have a Thetford commode. From what I’ve read they are a little more complicated.

Tom (@guest_260826)
27 days ago

My Dometic rv toilet uses a blade mechanism, I replaced the seal since the water in the bowl would leak out if it sat for a day. I got the new seal seated in the groove, greased the seal, turned the water on and I could hear it dripping into the black tank. After a few minutes, I decided to pull the seal out of the groove just a fraction of an inch, no more water draining from the bowl. Lesson learned, don’t assume that the seal needs to be seated fully into the groove.

Jim Johnson (@guest_260712)
27 days ago

O-ring silicone grease is inexpensive and in every plumbing section. It won’t harm rubber or plastic. My most frequent use is to periodically treat the joints in my waste lines. They are MUCH easier to connect and disconnect. It takes very little to do its job; just a dab on a gloved finger and smeared over the rubber gasket.

Jim Johnson (@guest_260709)
27 days ago

I discovered that there are multiple times I want to turn off the water to the toilet without shutting down the entire RV water system; bad valve, wanding, freeze conditions… On many RVs there is enough exposed PEX waterline to easily add a Sharkbite style valve. Even with no water coming to the toilet it can usually still be used via a water bucket or jugs.

Bruce (@guest_260625)
27 days ago

Looks easy, but video would have been super great! I’ll have to search youTube to see if I can find a video.

John (@guest_260900)
26 days ago
Reply to  Bruce

I concur. A video, with detailed explanation of the steps, showing and telling (not just music like some folks do these days), would be great. But this article was awesome as I always thought you had to remove the toilet to do the seal change.

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