Abstract: Drain/check valve of soft elastomer for floor of vehicle, resembles a musom. Top surface of mushroom head has radial grooves. Central passage through head terminates in a tapered flat edge of mushroom stem which is normally closed. Head is peripherally grooved in grommet-like fashion to yieldably accept edges of hole-defining floor surface or similar panel. With valve in place, elastomer between radial grooves extends radially inward beyond walls of passage below head, thus forming narrowest part of passageway. Passage diverges downward, when wide open, and passage in its preformed state is progressively larger in overall perimeter and towards the terminal lower end thereof.