I started the process of de-winterizing today and quickly got stumped . The water pressure from my home supply removed all of the pink from all of the water facets inside and outside until clear water...
first thought is the hot water tank. If you opened cold taps first run thru everything would look right. Second run, if you opened the hot tap you could be losing pressure to the heater. second thought is there is an open valve somewhere, not letting pressure build. put water in your fresh water holding tank and try pressurizing the system with your 12v pump. If all OK it should shut off and hold.