Last winter I decided to use air to blow out the lines with air, I had the problem that even after letting air blow through the cold water side of the kitchen faucet for more than 10mins (50psi and opening closing the faucet numerous times) I still could hear "gurgling" in the line. Since I could hear the gurgling I knew there must be water in the in the line yet, and since we live in Wisconsin and can get temps as cold as -30 and wind chills down to -50, I ended up using the good old pink antifreeze to make sure that I had it done right. I use 2 gallons to do our Grey Wolf, its about 1.25 to do the lines and the rest goes down the drains and the toilet.
When I put the camper in the shed of the winter I park it on 2x10s to keep the tires off the concrete, I also place dryer sheets all over inside the camper and also stuff them around all the tanks.
TT-2013 Passport 3220BH
TV-2004 F150 FX4, not exactly stock...
with 2001 Kodiak K215: 2010-10, 2011-12
with 2012 Grey Wolf 26BH: 2012-19, 2013-24, 2014-11, 2015-6
with 2013 Passport: 2015-13, 2016-15 booked