RV Toilet Seal Replacement

It was a hot fall day when we first noticed the smell. There was no doubt about the source – we had dumped far too many black tanks to have any question. The odor definitely came from the toilet. We checked the blade seal on toilet flap. Yes, it held water in the toilet bowl just fine. That meant it was the flange seal below the toilet that was allowing flumes to escape.

Flange & New SealWe ordered the flange seal for the Thetford Aqua-Magic IV from Amazon and set it aside until spring. Well, spring has sprung and we de-winterizied and flushed the tanks. We stuck a spray nozzle into the toilet past the flapper valve and turned it on.  That resulted in water (clean water thank goodness) all over the toilet floor. The seal replacement could not wait a day longer.

Replacing the toilet seal seemed intimidating.  But it turned out to be a very easy do-it-yourself job. We spent more time researching how to do it than doing it. Remove the toilet, a 5-10 minute job. The plastic RV toilet is very lightweight and quite easy to handle. Seal replacement took 30 seconds and remounting the toilet took 10-15 minutes. Cleaning the toilet to our satisfaction took about an hour!

Right Flange Nut - plenty of roomSo if you smell unpleasant odors in your bathroom and your toilet bowl does hold water without leaking, here is how you can replace the flange seal on a Thetford Aqua-Magic IV toilet (other brands are similar, but check). The space is tight in a Class B, so this job is probably easier for those with smaller hands. You have two nuts, one on either side of the toilet that hold the toilet to the flange. BE SURE TO TURN OFF THE WATER PUMP OR DISCONNECT FROM CITY WATER before you work on the toilet. And you have a water connection in the back. Remove the two nuts and water connection.  Now the toilet lifts straight up.  If your toilet does not hold water, order the complete seal kit and you will have to dismantle the toilet to replace all the seals (videos available on YouTube).  Remember, it is definitely less smelly to dump and rinse your black tank first!

Left flange nut - no roomThe right side of the toilet had plenty of room to swing a closed end wrench to loosen the bolt. The left side – to our surprise – was only hand tight. We found out why later. There is no room on the left to swing even the tiniest wrench.  Reaching the nut with your fingers is about all you can do.  A wrench with a two inch handle might do it!

Water ConnectionOnly our biggest adjustable wrench fit the plastic coupling on the water connection, but it was too big to swing. So we ended up using Vise-grips to loosen it. Then you can unscrew the coupling by hand the rest of the way.  As you can see from the photos small hands make the job easier.

Water connection at back of toiletHere is a photo of the water connection once the toilet is removed.  This flush valve assembly is another replaceable part if yours fails.  Should you decide to replace the toilet instead of replacing parts, measure the fit carefully.  The tight clearances in Class Bs might mean a new model will not fit!

New flange seal installed on toiletOnce the toilet is out, you can thoroughly clean the insides, then install the new seal on the toilet and reinstall.  By pushing down on the toilet you can compress the seal to aid in tightening the left flange nut without using a wrench.  Alternate tightening left and right sides to get a good seal.  You can check over time and tighten if needed.

We learned that working on the toilet is really quite easy and can be done by someone who is just moderately handy.  Of course these kinds of horrors show up just as you prepare for a trip, but this  one turned out to be no big deal at all.





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  • Florent 🚐

    Awesome explanation. Thanks. I have one question. What would you recommend using to completely cover the hole under the toilet in the event of installing a composting toilet?