Any chance you can give us more to go on?
What is not coming out to bad now that you've switched from winterize?
Are you saying when you are connected to city water that water backflows from your fresh water fill port?
If so, it sounds like a stuck check valve in the fresh water pump.
Unhook from city water (or turn off), open a faucet to relieve pressure, turn on your fresh water pump, open and close a faucet several times (to hopefully clean the debris from the check valve) turn off the pump, open a faucet to relieve pressure, reconnect (or turn on) city water, see if problem still exists.
Also, are you using a pressure regulator if connected to city water?
2016 Flagstaff 8529IKBS Diamond Package 5th Wheel-Goodyear Endurance Tires
2017 Ford F-Series SCREW 4x4 - Factory Puck B&W Companion
TST Tire Monitor w/Repeater - Sinemate 3500w Gen.
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