Abstract: An automatic toilet flushing system can be used in any existing manual flush toilet and comprises a first sensor for detecting toilet use, a second sensor for detecting filling of the toilet tank to a predetermined level, and a valve actuator linked to the two sensors for opening a toilet water inlet valve in response to a signal from the first sensor and closing the inlet valve in response to a signal from the second sensor. A toilet flush operating device in the tank is connected to the supply of water flowing into the tank and comprises a hydraulic piston and cylinder, the piston moving between a retracted position and an extended position in response to water flow into the cylinder. The piston is arranged to urge a flush lever arm linked to a flush valve in the tank in a direction to open the flush valve when it moves towards its extended position.