No luck, just common sense ... yes, rigid pipes like copper burst. Even PEX won't burst (well, maybe the fittings will be a problem if filled with water and frozen.
I've damaged hard plastic components, like the skimmer box and plastic valves on pool components, with frozen water, but I've never, ever, seen flexible plastic burst. I've frozen many aluminum cans in the freezer, but never seen a flimsy plastic water bottle with plastic cap fail after being frozen solid.
I simply don't believe anybody has ever damaged a flexible plastic tank or even a metal tank with just a few inches of water in it when the water has room to expand. Sure, rigid fittings are a different story, but damage to flexible fittings is even unlikely. Just make sure the fittings aren't filled with water ...
As a disclaimer ... I'm the type of person whom will always question what is usually the "accepted protocol". That is what makes me a pretty unconventional engineer and alienates many of my peers. But that is why my response to typical questions like ... 'what's the best way to deal with the awful tasting anti-freeze in my water tank' goes something like this 'Why are you putting anti-freeze in your drinking water when you probably don't have to?'
I'll never say that I am correct all of the time!
Of course draining the lines is necessary, but aside from that, what is the worry? Every fall, thousands of miles of flexible irrigation lines are simply drained and blown out all across the northland, with never a concern about the drips of water that will eventually collect in the low spots. We come back in the spring and the vast majority are damage-free without the use of anti-freeze.
