Next spring we'll see a few posts here about broken lines from those the blew out the lines but didn't get all the water out. Air can easily be forced through the low points without removing the water, then it drains back and freezes.
Never broken a line yet but then I use antifreeze or (usually) keep heat in the rig all winter since we use it every month or so.
2009 45' Magna 630 w/Cummins ISX 650 HP/1950 Lbs Ft
Charter Good Sam Lifetime Member, FMCA, SKP
RV'ing since 1957, NRA Benefactor Life, towing '05 Odyssey