The valve is integrated in the water pump. On the suction side of the pump is a strainer: isolate it, remove the bowl cover and clean the plastic bits out of the strainer. After reassembling run your water pump for a few minutes to flush the crap out of the pump that is causing it to backfill your tank.
This may need to be done again as more plastic shavings work their way out of the fresh water tank.,
Ted & Melinda
2016 ACE 27.1
2016 Chevy Sonic Toad
2020 Chevy Colorado Z71 Trail Runner Alternate Toad