Lynwood- only two common points between the fresh water inlet and the fresh water tank. One is the NORMAL/FILL select switch that directs fresh water to the normal water lines OR to fill the fresh water tank. I am trying to visualize a half way position of the 3 way valve that would or could allow siphoning to occur. May have to get pencil and paper and sketch out the possibilities. But doesn’t seem likely. Would seem water would flow into the tank when not siphoning.
Second would be the point the fresh water source pipe joins the fresh water pump/tank pipe downstream of the pump. Not sure exactly how that connection is made. The check valve would keep water from flowing into the tank. But I can’t really see a way that siphoning could occur.
