This is my basic setup for the water system in my 2004 5th wheel trailer. My 2008 OFF-ROAD POPUP is very similar except only has one sink and no shower or toilet connections and no gray or black water tank. I have to capture my own gray water and tote away in the popup.
My anifreeze hose is placed between the fresh water tank and the water pump. It is actually just a few inches away from the intake side of the water pump. Having the value located here selects either water coming from the fresh water tank or coming from the antifreeze hose.
With my system I cannot use the water pump to fill my fresh water tank. I have to manually fill it at the manual fill port...
Roy Ken