Abstract: A diaphragm valve for a toilet flushing mechanism, and a hydraulic flushing assembly using the valve, control water mains pressure for the pressure flushing of toilets with small quantities of water. Water mains pressure is used to retain a flexible diaphragm against the orifice through which flushing water from a pressurized tank can flow through the valve when flushing action is desired; flushing is initiated by temporarily lowering the water pressure applied to retain the diaphragm. Various designs of pressurized tank can be used to provide a constant or variable volume flush, which can be less than six quarts or liters.