Few RV subjects get as much scrutiny and exhaustive analysis as winterizing – protecting your plumbing from freezing when you store your RV for the winter, or just want to take it into freezing conditions. Here's my take on it.
I'm not an expert on winterizing – as a matter of fact, I winterized for the first and only time a few weeks ago. Normally I'm where the sun shines and the warm breezes blow, and don't have to winterize. I do know a bit about RV plumbing, though, enough to be convinced that I don't want to do any more of it than absolutely necessary. RV plumbing is a mess. The pipes are plastic, it's all hidden behind the cabinets and other permanently installed fixtures in your RV, and once it's messed up it's very hard to repair. I want my plumbing to live long and prosper so I can spend my time staring out over the ocean and thinking deep thoughts, not crawling around inside my cabinets, busting knuckles and getting frustrated.
There are a few simple principles I have discovered in my 40 years of mechanicing. The main one is to never take anything apart you don't have to. If it's working, leave it alone. I know it's tedious to flush all the pink antifreeze out of your system in the spring, but taking plastic plumbing fittings loose is a sure way to tempt the vengeance of the gods. They are compression fittings, and the formerly flexible material that made the seal has been baking in the heat and shivering in the cold for lo these many years since the RV was built. You aren't as flexible as you were all those years ago, and neither are your compression fittings. In addition, clean new parts assemble much better than parts that have been sitting at the bottom of a RV cabinet for a long time. They have burrs on them from the original assembly plus whatever more burrs you put on them taking them apart. Dirt gets into the fittings – there are all kinds of things to go wrong. A good, non-leaking fitting depends on two smooth, clean surfaces compressing a smooth, clean flexible material. Unless you're replacing everything, leave it alone. Sooner or later you'll break something.
Air and water are different – I went to school long enough to say that with confidence. Air is compressible, water isn't. As a result, you can blow many cubic feet of air through an air line and still leave water in it – enough water to collect at a low point or bend or fitting and break your pipes when it freezes. Unless you have a dehumidified – not just dry – source of compressed air and blow it through a line for half a hour, you are leaving water in the lines. The only effective mechanism is evaporation, and by the time your lines are dry you will have stressed them so much it will be a miracle if they hold water next year. Water pump diaphragms will flap around wildly as high-speed air goes by them, so any weak spots in them will get damaged as well. Compressed air in your water lines is a very bad idea for the RV owner, despite its appeal to the RV mechanic wanting to take a few shortcuts. He'll be glad to sell you a new water pump next spring, by the way. Water lines and pumps are designed to handle liquids like water and RV antifreeze, which they do very well. Don't ask them to do things they aren't designed to do.
Here's a novel idea – put pink RV antifreeze in the fresh water tank(s) and use the water pump and gravity to circulate it throughout the system. When you see pink antifreeze come out of each faucet, you know for a fact that there's no water in that line. Antifreeze travels through the system just like water does, pushing the water ahead of it. Circulate the pink stuff through your pump return lines by opening the city water valve. Pop the check valve at the city water intake to get all the water out there. See? It's simple. If the idea of pink stuff sitting in your fresh water tank gives you heartburn, drain the tank after you finish winterizing. This revolutionary technique will save you lots of broken plumbing, which is the whole idea of winterizing in the first place. Man, I oughta patent this stuff…