Having two working check valves below the “Y” connector is very critical to the operation of the backup pump. For example, if the check valve is bad above the main pump, the water will not get discharged by the backup pump if it has to activate. The water will only go up the “Y” connector and then come down through the main pump‘s discharge pipe. The check valve above the main pump must be working and installed properly in order for the backup pump to operate.