Larry-NC

Hi Larry, I see you answering a lot of questions on this forum, so you seem to know what you're talking about; We have a 2015 FR 26ft. Palomino Puma bumper pull we bought used in 2019. The owners told us they never hooked up to city water; they always used the Fresh Water tank. On the 2nd or 3rd day of camping I check my tank monitor and the Fresh Water tank is filling up. YouTubed it to see why, and several people said to disconnect city water, run faucets and water pump alternately on and off several times to clear the water pump opening so it will close right and stop the city water from drifting into the FW tank. Then reconnect to city water. I've done this several times. This did not work for me. My question is "Can I turn those knobs on the water lines near the water heater to block the water coming from the city connection into the Fresh Water tank and still use city water plumbing from rv park connections?" Appreciate your answer. Thanks, JG