The tank vent and toilet drain enter the holding tank from the top and the drain outlet exits at the lowest portion of the tank. In some cases, the vent can be cut with a hacksaw or disconnected from inside the cabinetry. The toilet simply unbolts from the floor flange, then the flange (which may be connected to the tank in a variety of ways), is simply removed from the top of the tank. The same for the drain outlet on the holding tank itself. It will ultimately terminate and connect with the other holding tank at a location near the left rear side of the coach. All termination valves are removable so you simply remove that pipe and valve associated with the tank in question and reverse the process for installation.
Wish I could provide more clear-cut instructions, but without seeing the actual installation it’s nigh impossible to respond fully. But I hope this little bit will help!