A liquid waste disposal and canister flushing system includes a cabinet (6) with a sink (14k) for receiving the canister (4) and a subsink (141) for receiving a lower portion thereof. The subsink (141) is connected to a drain line (14o). A plunger subassembly (12) includes a plunger rod (92) and a stopper (95) which functions as a drain valve for the canister (4). An injection jet (34) is connected to water and cleaning solution sources (21, 39) and discharges diluted cleaning solution into the canister (4) for flushing same. The injection jet (34) engages the plunger subassembly (12) for ejecting the stopper (95) from a canister drain opening (12a). A control system (10) includes a programmable microprocessor (50) which can be programmed to provide drain and flush cycles of predetermined duration. A number of different container and accessory embodiments are disclosed. A method of liquid waste disposal and canister flushing utilizes the microprocessor (50) for delaying the flush cycle until completion of the drain cycle. The control system (10) can provide drain and flush cycles of predetermined durations, can monitor water pressure, flow rate and temperature, cleaning solution flow rate, holding tank neutralizer inputs and timing and other system parameters.