Abstract: A method for introducing liquid agents, such as cleansers or disinfectant, into the water supply of a sanitary facility, such as a water closet includes the monitoring of the pressure characteristics of a flush cycle and determining an appropriate time during the cycle for introduction of the liquid agent. A subsequent flush cycle is similarly monitored. At the determined time the agent is added. Preferably, the determined time is towards the end of the flush cycle. An apparatus for carrying out the method includes a liquid reception, a pressure sensor located in a line connecting the reservoir to the water supply line for the sanitary facility, and a control unit which operates either a pump or a valve. The liquid can be introduced into the water supply either by the pump or by suction.