What have you got against RV antifreeze? It's inexpensive and, unlike automotive antifreeze, it's not poisonous (although I wouldn't drink it). It's normal practice to disinfect the water system after a long period of disuse, and to do this, I run a full tank of bleach/water mix through all the lines and follow that with a full tank of fresh water through all the lines. There is NO antifreeze remaining anywhere in the trailer when I'm through.
But, Gary's solution is perfectly sound too. I've done it that way one winter and had no problems. I don't think you even have to blow the lines out. If you open all the faucets and all the drain valves in the lines in the trailer, and empty the hot water tank, there will be so little water left in any of the lines that freezing is not a problem. But, there WILL be water in the U-traps under the sinks and shower pan that should be protected with antifreeze. It will be difficult to blow them out completely. I've tried doing it with a plunger, but there's some water left. My toilet has just a straight pipe into the black tank, so there's nothing to freeze there.
- Jack