I thought of an item that I SHOULD have thought of about 2 decades ago..... oh well.

RV antifreeze.

If the house heat goes out for a long time, I know to drain the water supply plumbing but had forgotten about the water in the sink drain traps.

Some RV antifreeze down the drains and the toilets (after flushing and draining) should save that plumbing from freeze damage.

Bought some this weekend.