Two common problems with the toilet are 
Water supply and/or shut- off doesn't work correctly, and 
Fresh water leaks around the base of the toilet. 

Here are instructions for fixing both:

1 - remove the panel behind the toilet (7 plastic caps atop 7 screws). 
2 - Remove the short water line at the T. 
3 - press the pedals down and remove the nut on the front bolt. 
4 - Remove the round "peephole" cover under the seat and look down and to the right for the rear bolt. You can remove that nut with either a socket set with extension and an offset "wobble" socket, or reach it from behind with a wrench. 
5 - Lift the toilet out and lay it upside down. 
6 - Remove the screws around the metal plate along with the other two, then lift off the plate. 
7 - Remove the screws around the next layer below the previous plate and you can separate the sections of the toilet. 
8 - If your toilet water supply does not operate properly, replace the foot pedal-actuated shut-off valve with one from an RV shop. 
9 - If your toilet leaks fresh water around the base when flushing, you need to seal a hole in the little rectangular box where the two hoses attach. To do so: 
a) remove the seat by pulling the plastic keepers sideways from their mounts. 
b) b) push the seat mounts forward and slip them through the housing (the rectangular box is attached to these mounts. 
c) c) remove the 10 screws from the top of the box. 
d) d) discard the little plunger and shriveled seal (the reason it leaks water.) 
e) e) using epoxy glue and a nickel (5 cent piece), seal the hole shut. 
f) f) reassemble toilet and put a little Vaseline on the rubber sewer ring before reinstalling it. 

John Elliott