I usually blow mine out ( pain in the butt ) then do 3-4 gallon of antifreeze. I know belt AND suspenders,$12-$ 16 is chump change, seems like everything RV repair wise starts at $600.
However, I could use some advise. I have a plug with a tire core valve that screws into the water inlet. I would like to find a connection that I did not have to push in and hold, to air up the system. I never seem to get it filled. It's like hold the air hose, go inside open one drain. Come back out, repressurize, go n and open one more valve....about 10 times going in and out. Then it sounds like there is water gurgling in the line somewhere.
2007 Newmar KSDP. 3912
2010 Nissan Frontier SE