Originally Posted by TG Twinkie
I eliminated the drain valves as they are rarely in the lowest part of the plumbing system. Use compressed air to evacuate the water.......
TG's got it right. The extra valves spread all over the coach are IMHO totally unnecessary if you're using compressed air to evacuate the system.
I don't add antifreeze to the drained fresh water tank. Fore and aft plus low side draining has worked well in the past. I feel there is plenty of room for expansion in that large of a tank. I find it takes forever to get the antifreeze taste out of the water. I do add it to the sink and shower traps. All of mine were damaged by the PO not taking this simple precaution.
Dump the drain valves. Simplify wherever possible.