So another part of the drill is if they are going to evacuate, we need to remind them to drain their systems out - and even then, they need to check J and P traps and other low spots in their plumbing systems for cracked pipes.

In a well designed and built system both supply and drains, excepting the traps of course, drain dry once the caps are removed. In very cold locations it sometimes pays to invest in some drain antifreeze, typically propylene glycol as it is non-toxic. A splash down each drain protects the traps and avoids the unpleasantness of finding out a trap, even worse the toilet, froze and cracked.