If you are talking about the tank fill valve it should be in the wet bay usually near the city water inlet. It should be in the "fill" position only when filling the fresh tank.
Then there is a valve on mine near the water pump that should be open to allow the pump to pull water from the tank. This valve is probably located near the suction hose used for winterization. You need to have the valve from the pump to the tank open and the valve from the pump to the suction hose closed. Now you can use either city water if you are hooked up, or if not, by switching on the water pump. I hope this helps.
2005 Newmar Kountry Star Gas 3742
Workhorse W24, 8.1L/Allison 5-spd
JT, Em & the boys, Kong and George (rescued grey tabbies)