A vacuum cleaner has an electric motor driving an air impeller (74) for creating suction and a pump (104) which draws liquid material through an inlet tube (310) from the bottom of a tank (32) and expels it from the tank. The vacuum cleaner also includes a mechanical shut-off and override assembly (144) that automatically shuts off the motor if the liquid level in the tank gets too high. A user, however, can mechanically override this automatic shut-off in order to continue pumping liquid out of the tank. A priming apparatus is disposed in the tank in fluid communication with the pump, and a valve is selectively actuable to establish a pressure differential across liquid in the priming apparatus to thereby prime the pump.