SpongeW ... I have a pretty good system for draining the pipes. Well .... obviously not good enough.
Pipes are all installed inside the heated area, not in the walls. So they are easier to heat and repair.
All pipes are all pitched towards the multiple valves at the bottom. You can drain the whole thing in 5 minutes.
I fill all traps with antifreeze.
The problem comes from the tankless water heater. It drains really fast, and doesn't waste water, which is why I went with it. But sometimes it seems to "hold on" to a little water, which it then releases slowly. That water ends up right above the heat tape.
It seems like it's only a problem when the power goes out and it's really cold/windy.
I should get a propane set up that doesn't require electric. It's another one of a million things I should do, but haven't gotten too.