Abstract: A ball valve for controlling upstream to downstream fluid flow, for example, from an apertured tank bottom, has a housing body for bolted-on mounting. The housing has a flow passageway therethrough that angles between its upstream and downstream portions and that is controlled by a valve ball rotatably positioned in and sealed-off within its upstream portion. A resilient, L or ladle-shaped annular gasket is positioned upstream at the joint between the valve housing and the tank bottom and in engagement with the ball adjacent an upstream end portion of its open-end flow passage and, in such a manner as to maintain the flow area of such passage.