I have an older trailer with a Thetford toilet, model# Aqua Magic SL 8420. It has the exact symptoms you describe. I have replaced the base gasket to no avail. I did see that the hose connecting to the opening in the toilet that the water comes out of when flushing the foot pedal has a failed gasket where the hose enters the housing. It appears this is the culprit. All other connections seem good and tight. I would like to know if this is what you found as the problem and if parts are available for this. My model is probably 25 years old, although maybe parts are still available. I plan on calling Thetford tomorrow.... hope u got it fixed. Please update this thread so we know what u found. I will do the same.
I had a similar leak on my toilet. I traced it to a small crack in the anti-siphon valve on the back of the toilet. This allowed a few drips of water to leak everytime the bowl was filled. Replacing the valve was not difficult to do and I did not need to remove the toilet from the base.
The leak is coming from the back of the water module and only leaks when you flush with the pedal. I am going to pick one up and change it. Hopefully I won't have to remove the toilet to do so.
If you go to Thetford.com you can download all kinds of repair procedures for their toilets.
Click on Products, then on Permanent toilets.
Click on the model that you need and go to Manuals. A whole list of repair pages can be downloaded.
Alex
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