A method of dispensing detergent in a dishwasher having a wash tub that includes a fluid reservoir to hold a treating chemistry, a lid operatively mounted to the fluid reservoir, and is configured to move between an open position and a closed position, and a hydraulic actuator is fluidly coupled to a fluid source and configured to initiate movement of the lid between its closed and open positions in response to fluid pressure applied to the actuator by the fluid source.