We have a Dometic toilet. The flush recently broke so I needed to get into the tank to fix it. I removed the control panel and can see the top of the tank, but just not enough room to do any maintenance. The loo had to come out. I could not find anything useful on line. The base has 6 screws accessible from the outside. The rear of the toilet is hooked onto a bracket, but the fill pipe will not allow it to be lifted off. eventually I found that by removing the ducting at the base I could twist it off.
After that it could be fully serviced and cleaned.
A Thetford would be similar but may have YouTube help
John
PS, ignore the above, wrong advice for a C2 😡