Abstract: A flow control valve is provided for connection to a water supply line for ontrolling the flow of water between a water tank and a toilet bowl in an aircraft. The valve comprises a valve housing having an axial bore therethrough. A cylindrical valve member axially slidable within the bore is moved between a normally closed position against a valve seat and an open position spaced from the seat. The valve member also has an axial bore therethrough. When the supply line is pressurized, a float in the bore of the valve member moves against a seat in the valve member to completely stop flow through the valve when the valve member is normally closed. When the supply line is depressurized, the float moves away from the valve member seat by the force of gravity to permit draining of the supply line.