1. In combination with a pickup truck having a rear pickup box with wheel well covers projecting into the box and positioned between the ends of said box, and a camper with plumbing therein mounted in said box with an external lower side wall of the camper extending substantially the length of the box, disposed inwardly of a wheel well cover, and spaced from an adjacent side of said box, a holding tank positioned between said camper''s lower side wall and said adjacent side of said box and disposed toward an end of said box from said wheel well cover, a drain conduit for draining said plumbing and means detachably connecting said drain conduit to the plumbing of the camper, said drain conduit communicating with the interior of said tank adjacent the base of the tank, said drain conduit with release of said means detachably connecting the drain conduit to said plumbing being adjustable to provide for drain flow under gravity from said tank, and vent conduit means connecting with said tank extending upwardly along the outside of said camper.

7. An assembly for collecting waste liquid from the exterior drain opening of a camper unit supported in the box of a pickup wherein said pickup has an internal wheel well cover, the assembly comprising an elongate hollow tank with opposed side walls, opposed end walls, and a top and a bottom providing a substantially enclosed storage space, one of said end walls including an inclined bottom portion adapted to be positioned over the wheel well cover of a pickup, and a pair of flexible conduits joining with said tank, one conduit having an end connecting with the interior of the tank adjacent the base of the tank and the other conduit having an end communicating with the interior of the tank adjacent the top of the tank, said one conduit including an end opposite the end communicating with said tank provided with a coupling for detachable connection with an exterior drain opening of a camper unit.