Usually when this happens, the check valve just inside of where you would connect your hose for city water is a little bit askew and not seating properly. With your pump turned off and the water pressure relieved from the system, stick a pencil or screwdriver or something of similar size into the city connection to see if you can push the center stem of the check valve in a little so it will spring back and seat properly. If this doesn’t work and you want to just take care of it for the short term, put a 3/4”MHT hose thread cap onto a 3/4”MHTx3/4”MHT hose thread coupling And thread the coupling into the city water connection. If you don’t have access to a hardware store, get out one of your hoses, connect it to the city connection and kink it shut. Keep it kinked with a zip tie or string or whatever else you can think of.
2016 Rockwood Windjammer 3029W Diamond
2015 Chevy 3500HD LTZ 6.0 Crew Cab 4x4 Long Bed 4.10:1 SRW