I know most people from the coast blow them out but our temps in the interior get much colder. I have never had it get into my water tank but did in the hot water tank if I didn't switch the by pass valve. I bought a motorhome in Alberta that they said had the lines blown out and one froze under the floor and I had to rip out the floor to replace the line.
Yeah, I blew them out really well I thought. I drained the HW tank. I also ran antifreeze through the sinks to clean out the p traps. Turns out the pump is OK but the strainer had enough residual water in it to freeze and crack. So now I have a spare pump.
In the past I've added anti freeze to the main water tank and filled all the lines by running taps, but I got away from that several years ago when I acquired an adaptor for my shop compressor to hook up to the water system. But that method is messy in the spring because you need to flush your main tank several times to clean out the antifreeze. I guess I'll have to go back to that for future storage.
