Quote Originally Posted by Fentonite View Post
There was no bypass on the original plumbing, not even a valve (so I added a valve at the inlet to the water heater tank). There are drain valves at the low point of the hot and cold lines, and a petcock to drain the fresh water tank. I haven’t drained the black tank yet. There’s no grey tank on this rig. I figure I’ll just drain the system before it freezes.
Drain, blow out with 40-50 PSI air and introduce RV antifreeze...and blow again while working any valves, faucets, etc. Antifreeze in the p-traps too.

Even a blown out system can retain moisture in the valves and freeze.

15 years without an incident doing it that way. Maybe it's overkill, maybe not?