Always wondered about water freezing in the P-Traps and why it would hurt anything at all.
Its the expansion that damages things, like a full hot water tank or a pipe.
If the freezing water has no where to go when it expands that's how it bursts things.
In a P-trap wouldn't freezing water be just like an ice cube in a tray, it's not contained at all so why would it damage anything? Probably some water left in your HW heater after its bypassed and drained.
Mine still get plenty when I'm running it out the faucets regardless.
2017 Open Range - Light 297RLS, BX1 Gooseneck
1997 Dodge Ram 2500 CTD LB 4x4