[rohrmann]

If your pump still works, a cheaper and possibly easier fix would be install a check valve in the pump pressure side line. This will not affect the performance of the pump and will permanently fix the issue. I made this fix years ago while at the rally at Seven Feathers in 2014. Originally, I had installed the check valve on the suction side of the pump, where the white coupling is behind to the left of where the brass check valve is in the photo. I discovered the suction side fittings can not handle the pressure and I had a water leak at the pump. I replaced the original check valve with the coupling and installed a new check valve in the pressure side line and have had no issues with the tank filling past the internal check valve of the pump. All the new fittings are shark bite type fittings.