If it uses a gravity fill there will be a small locked cover head high or so.
If it doesn't use gravity fill then in the 'wet bay compartment' should be a panel with valves/switches that you change position to use 'city water' OR to 'fill' when hose is connected
If you don't have a 'wet bay' with water panel then you may have valves located at/near water pump (inside a cabinet/under bench seating)
Connect hose to city water...
Then suction side of pump could be 2 valves....one allows city water to flow thru pump----other allows water to go into fresh water tank.
PITA because there are also other valves on discharge side of pump
Easy when you KNOW but pain when you have to trace lines out.
Good luck!
Is it time for your medication or mine?
2007 DODGE 3500 QC SRW 5.9L CTD In-Bed 'quiet gen'
2007 HitchHiker II 32.5 UKTG 2000W Xantex Inverter
US NAVY------USS Decatur DDG31