Abstract: The pump has a pumping chamber with a deflectable diaphragm member and fluid inlet and outlet passages. A deflectable valve flap is disposed across the fluid inlet passage and another flexible valve flap is disposed across the fluid outlet passage. Movement of the flexible valve flaps is responsive to movement of the flexible diaphragm member, reciprocation of which establishes alternate sequential suction and discharge conditions. An air chamber provided in the pump receives outside air through an air vent opening and also communicates with the pump discharge passage through a bleed hole when the outlet passage is closed by the outlet valve flap. The outlet valve flap is also deflectable to a position where it closes the bleed hole. Under this arrangement, continuous siphoning of fluid through the pump after the pump has been shut down is obviated.