Some folks just use air and get by with it year after year.
I also believe that it would be possible for water to collect in
a low point and freeze even after blowing out.
I do both-- in my trailer there is a little "dead zone" in the
water heater bypass area. This short length of hose does not
get antifreeze when in bypass mode.
I drain my WH and leave the plug out.
I blow the system with air while the bypass is in normal use mode.
Then I switch to bypass mode and pump in RV antifreeze using
the onboard pump.
The whole process takes me 30 minutes and a gallon and just a tad
more of antifreeze.
In the spring we flush lines briefly and for the first couple of trips
we use a blue jug for fresh water for drinking and coffee.
After that, the minimal taste is gone and we can use the water
system for making coffee and drinking.
Dan & Rita D
2004 5.3L Silverado 1500 ext. cab 2WD
1999 Suzuki Intruder Motorcycle
Blue Ox WD hitch, AirLift load levelers
Camping days 2010-53, 2011-47, 2012-41,
2013-41, 2014-31, 2015-40, 2016-38