A valve assembly for a fluid-containing tank (20) and method of making same are provided wherein such valve assembly (21) has a flow passage (33)therethrough and such flow passage has a central rectilinear flow axis and an inlet (31) and an outlet (32) which have central axes common with such axis. The valve assembly (21) has a valve member (35) which is operable from the bottom of the tank (20) and is movable between open and closed positions thereof and once moved to its open position enables substantially free unobstructed flow of fluid through the valve assembly (21) parallel to the axis and with minimum pressure drop to thereby enable a maximum rate of fluid transfer through such valve assembly (21), and the inlet (31) is adapted to provide complete drainage of fluid within the tank (20).