Fixing a Leaking RV Toilet

RV ownership certainly has its pros and cons. One con of RV ownership is maintenance with toilet and black tank repairs being, perhaps, the biggest and smelliest con of all. As you know, RV repairs can get expensive with the shop rates varying between $75 and $129 an hour. Fortunately, many RV repairs are simple and can be done by anybody who is handy with tools and who possesses a little common sense. One such repair is a leaky toilet. I recently had to make this repair and I’m going to show you how quick and easy (and cheap) it is to do.

First you need to determine the source of the leak. Does it leak all the time or simply when you flush? If it leaks only when you flush it’s usually one of two things, a bad water module assembly or a loose fresh water connection to the toilet. Obviously, you’ll first want to make sure the water connection is good and tight. Over time, vibrations and temperature variations can loosen it so check this first. Unfortunately, this is easier said than done. Often, the amount of room behind a toilet where the connection is located is very limited. The solution to this is a small mirror and a basin wrench. Pictured below, the basin wrench allows you to tighten a horizontal plumbing connection quickly and easily when space is limited.

If the water connection is good and tight and you still have a leak, then the likely source of that leak is a bad water module (this was the case for me). This part is plastic and like all plastic has a tendency to become brittle due to age and heat. You can buy a repair kit, which includes a new water module and a new toilet seal, for around $22 on For my Thetford Aqua-Magic V, I purchased the Thetford 31705 Water Module Kit. If you don’t have the time to order this kit through the mail, you’ll have to buy it at a RV parts store like I did. I paid $41 at an RV parts store in Flagstaff. Ouch!

Like any job, you need the right tools to complete it. The most important tool you need for this job is the aforementioned basin wrench. Most people don’t have one of these in their tool box so if you have a family member or friend who has one, borrow it. Otherwise, you need to buy one like the Tekton 12 Inch Basin Wrench. For this job, you’ll also need a Phillips screwdriver, a 1/4 inch wrench, and a couple rags.

To repair the leak you’ll first need to shut the water off and drain the toilet. Next, remove the two nuts connecting the toilet to the floor. Then disconnect the fresh water line flair-it fitting from the toilet using the aforementioned basin wrench. After the fresh water line is disconnected, you can remove the toilet (make sure you have a rag ready to wedge into the hole to keep the odors out).

A basin wrench is an essential tool for this repair.
Bathroom floor with toilet removed.

Replacing the old water module with the new one is very easy and can be done in 10 minutes. First, flip the toilet upside down so you can work on it. Remove the retaining screw with a Phillips screw driver then pull and twist the flush tube off the hose barb of the water module. Next, lift the water module locking tab to release the water module from the toilet, then pull the module out of the groove. Angle the water module to disconnect the wire link from the lever arm hole. That’s all you need to do to remove the water module. Reverse the steps to install the new one.

Newly installed water module.

The water module kit you ordered also includes a new closet flange or toilet seal. Even if the old seal looks good, it’s a good idea to remove it and install the new one. Seals become stiff and brittle over time and replacing it with a fresh seal just makes sense and can prevent another potential source for leaks in the future. It only takes a few seconds to install the new one.

Once the new seal is installed, remove the rag keeping the tank odors out of your RV. Then reinstall the toilet using the original nuts (note, that the toilet will sit about an inch high before the nuts are tightened. This is normal as the new seal is holding the toilet up. After the new nuts are installed, the toilet will seal and sit flush with the floor). After the toilet is remounted to the floor, reconnect the fresh water line flair-it fitting to the toilet. Flush test the toilet and check for leaks. Now you’re done.

As you can see, fixing a leaking toilet isn’t rocket science. Anyone can do if you have the will, a little know how, and common sense. This repair took me 30 minutes, including clean up, and saved me big bucks. The money I saved can be used on other things like a new pair of hiking shoes, a new fishing pole and tackle, or a night on the town with the wife.

About Mello Mike 878 Articles
Mello Mike is an Arizona native, author, and the founder of Truck Camper Adventure. He's been RV'ing since 2002, is a certified RVIA Level 1 RV Technician, and has restored several Airstream travel trailers. A communications expert and licensed ham radio operator (KK7TCA), he retired from the U.S. Navy in 2004 as a CWO3 after 24 years, holds a BS degree, and now runs Truck Camper Adventure full-time. He also does some RV consulting, repairs, and inspections on the side. He currently rolls in a 4WD Ram 3500 outfitted with a SherpTek truck bed with a Bundutec Roadrunner mounted on top.

1 Comment

  1. Changing the toilet to a Nature’s Head composting toilet would be much more simple and you would never want to see a dump station again!

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