Abstract: A main pump unit which includes a main pump and a standby pump in a tank is placed on the basement floor, not in a sump. The tank is sealed with the floor level drain, preventing reverse sewer water from flowing onto the floor. The pump (main) turns on before the sewer water from overflowing the appliances, such as toilet and bathtub. The system includes an arrangement for using the customary fresh water supply for testing the pump. It also includes means for ventilating the tank to the exterior.