An outlet assembly for application to hoppers of railroad hopper cars and the like in the form of a frame made up of spaced pairs of longitudinal and transverse frame members joined together and shaped to define a continuation of the hopper car sheets, and slidably mounting a door plate or gate for movement between open and closed positions, in which the gate is a planar member of one piece molded construction formed from an ultra high molecular weight polymer and includes integral racks on either side of same that mesh with pinions journaled in the frame and reversably drivable, using conventional power equipment or the like, to move the gate between closed and opened positions. The gate assembly is equipped with a sanitary top seal that is in wiping engagement with the gate and is arranged to permit the lading when present to help provide the sealing action at the gate. The assembly also includes a positive gate stop to prevent accidental discharge of the gate from its trackway on being opened, and an automatic gate lock which operates to lock the gate in closed position when the gate is returned to closed position after having been opened.