On our cross country trip a couple of weeks ago we had a problem with water leaking out of the city water hookup whenever the pump was on. I found the solution to the problem on another site. Apparently, if you depress the check valve with too much pressure in the system, it will blow off the o-ring inside the valve. The fix was incredibly easy. Just remove the metal screen at the connection, pull off the plastic valve keeper being careful that you don't lose the spring, and then from the inside remove the pex connection and push the valve out. Reinstall the o-ring and reassemble.