Toilet attachment to holding tank
Toilets are attached to a location by a fitting known as a closet flange. These ABS flanges are made for 4 inch pipe but reducers can reduce the pipe size to 2 or 3 or 4 inch. I have used 3 or 4 inch pipe. The usual method is to locate tank in a fashion that there is a straight drop into any part of the holding tank. A test hole is made thru floor into top of tank. Flange pipe size is decided and gluded into closet flange. A hole the size of the OD of the pipe is made into holding tank. Pipe length is about 3 inches into tank. A hole about 1/2 inch larger than the closet flange is made in the bus floor. The flange is carefully located in position, considering the toilet 2 hold down bolts. The flange is screwed into holding tank with stainless steel round head screws. I have been using polyeurethane caulking, in a big caulking gun. This material is forever. After tank is secure, in position, 2 toilet hold down bolts are placed onto closet flange, anda wax toilet seal is positioned on flange. The toilet is carefully lowered onto wax seal. The toilet hold down bolts are slowly tightened. House hold and RV toilets are held by te same 2 bolts altho the bolts are in different locations. Care should be used to tighten toilet in place. The RV toilet bolts are in some difficult to reach locations. Facing the toilet, the left hold down bolt is under the toilet seat and requires a 3/8 drive ratchet, an 18inch extension, and a 1/2 inch universal socket, or a universal joint with a standard socket. Some hold down bolts use 1/4 inch bolts and some use 5/6 inch bolts. The RV toilets are fragile. The RV toilet also has a hold down bolt under the foot pedal on the front. Sometimes a small block of wood can be used to keep pedal out of the work area. A straight open end wrench will tighten this bolt nicely. Check the toilet of a firm attachment, with no wobble.
When installing the water supply line to toilet, at the rear of the toilet, I install a ball valve to turn water off at toilet in case of some problem and also a kitchen sink hose and spray valve within easy reach. The spray is great for any small bowl cleanup needed. I often use 3/8 nylon air brake line for the water supply with compression fittings. The ball valve is plumbed first followed by a line connected to toilet and finally the spray.
This about all I know. Frank