I just sanitized mine a couple of days ago, and was curious to see if I could blow any water out after completely draining.
I ran the bleach water through the faucets, so drained the Grey tanks and then pulled the "low point drain valves". I let it drain all night.
The next morning, after closing all the faucets and Grey tank valves, I hooked up a blow out adapter to my tank fill opening. Being cautious, I only ran about 45 psi through the lines, but would say it only pushed about a tablespoon of water out the low point drains. Not sure if that was because I needed more pressure or just a good design on the coach. As a result, not sure I'll use antifreeze in the lines, maybe just down the drains.
Thanks, Steve & Deb
2016 Coachman Concord 300DS
-Safe-T-Plus | Garmin RV 660 MLT
2008 Jeep Sahara
-Blue Ox base plate | Ready Brute Elite