Abstract: A removable waste fluid holding tank for use with a vehicle. A pair of U-shaped supports straps are suspended below the body of the vehicle with the base portion of the strap farthest inwardly from the side of the vehicle lower than the other strap. The tank is constructed to rest on the straps under the body of the vehicle and has an indentation in its base for receiving a portion of one of the straps to inhibit horizontal removal of the tank from the straps. The tank has inlet and vent connections at one end thereof to which drain and vent conduits may connect the tank to plumbing in the vehicle. Within the tank a conduit connects the inlet opening with the base of the tank. A handle is provided for lifting the tank slightly to release it from the strap, allowing it to be pulled horizontally therefrom after such release.