I've had the issue with my fresh water tank filling when hooked to city water. The pump check valves were leaking just enough to fill the tank in a week. My pump is a Remco Aquajet 55 so I disassembled the pump and rotated the 5 rubber check valve disks 180 degrees and this stopped the leak, for about a year then the leak stated again. I ordered the valve housing and replaced that and the pump has not leaked in over a year. A new pump is about 180 bucks and the valve housing was 30 bucks and about an hour of my labor.