Originally Posted by Seagimp
Well how does using compressed air blow out part of the line?
I've had no issues (when I was in the north and needing to) with either antifreeze or blowing out lines...
Reality for blowing out lines - you don't need to get every drop of water out. the problem with freezing is expansion - ice takes more room than water. As long as there is no point that can't safely expand - a little water freezing isn't an issue...
Antifreeze down drains is important as traps can freeze in a way that expansion has no place to go - but the normal feed lines being 'mostly empty' is perfectly fine.
I typically drained fresh water tank, bypassed and drained water heater, connected airline (regulated to 35psi) to city connection and opened each faucet (don't forget toilet and outside shower) one at a time until only air came out. I poured a gallon of antifreeze - splitting between each drain and toilet - getting into each trap, toilet bowl, and flowing into gray and black tanks (again tanks themselves not being an issue - lots of room to expand - but wanting antifreeze in line between tanks and dump valve.)