We have a Thetford Aqua Magic II and had to replace the valve. Need to fix anything? It's all there somewhere on the internet... Watched a Thetford vid that showed a nice looking young lady show how to simply tug on the pedal to get it off. No explanation how to re-install it tho. Putting it back on isn't easy and you need to get your eyeballs close the the rear of it to make sure all the parts are lined up before giving it a whack to go back on. Took me numerous attempts to do it. The instructions that came with valve kit were useless on how to put the pedal back on.
So I installed the new valve and foam gasket. BUT now, not only does it make a loud clicking noise when the pedal is pressed all the way down, the valve leaks a lot of water all over the floor when you press the pedal. Now I get to pull the toilet out again and see what's wrong. Pffft. :M
Maybe the solution for a defective Thetford toilet really is to just get a whole new Dometic one. Lemme know how the new biffy works out.