TOILET PROBLEMSThis is something that no one likes to talk about, but most of us have to face eventually....a toilet bowl that does not hold water.
Usually, this is caused by "debris" on the rubber gasket that creates the water and air-tight seal.    Use the end of a paper clip to gently clean the groove in the rubber seal.    You will have to have the toilet in a "flush" condition (flapper valve open), so it is a good idea to completely dump and drain the black water tank first.    Also, turn off the water and water pump.
The key to avoiding this nasty chore is to make sure that ALL the solid material goes down the drain BEFORE the flapper valve is closed.
In most cases, this will solve your problem of the toilet not holding water - and attendant foul odors, especially while going down the road.
However, if your toilet still does not hold water after a thorough cleaning of the rubber gasket, then you may need what Thetford calls an "Upper Mechanism Assembly".    Note that this assumes you have the Aurora model toilet.
If you suspect that you need a new part or need professional assistance, note that your Thetford toilet has a 2 year parts and labor warranty.    Also, Thetford is very liberal in applying their warranty, so even if you are out of warranty, give them a call and see if they will help you out.
If your toilet is leaking water on the floor, first check and make sure that all the water fittings are tight.    If you are still having problems, then the likely problem is either a water control valve (most likely) or the siphon valve.    Both of these parts are available from Thetford and are not too difficult to replace.
After two years of full-timing with the Thetford Aurora toilet, we had to have the Upper Mechanism and the water control valve replaced.    Both were covered by Thetford.