Key words, DONE PROPERLY… Now how would you have blown out lines plumed to an external shower with no shower installed… mine was per-plumed and framed for a shower and I didn’t know it… some are pre-plumbed for a washer the same way... I installed the shower after I found the piping already installed when I replaced the tub…
JaxDad did post how to properly blow them out with air, but truly there is no one size fits all, which is how the air only advocates make it sound…
I also know a guy that winterizes about 200+ RV’s every year and is responsible for the repairs if there is a problem come spring, he does them all like I do (a tip I got from him years ago)… if the owner insist on air only against his recommendation they sign a waiver… at least two of the dealers in the area use AF and air for winterizing but they don’t blow the AF out…
As I said there are choices and I made mine and that is also my recommendation and opinion…
I also know those that just use air and haven’t had a problem yet… that is their choice… there are a few that have used air only and reported problems right here as well as a few that used AF only and have reported problems…
And every year the air only recommendations flow like water some using only small 12V compressors none including what properly means… and every spring the leak post flourish…
While I can’t say for sure I believe there is some correlation there that reinforces my opinion even more each year…
I believe my method has covered all the bases of small compressors to no mixing of the water with the AF… and is a good way to do it…