I'm suddenly wondering why my tub trap didn't freeze but the washer trap did.
I'm in the process of moving the washer trap into the wall above on another thread.
But while I was back down under floor looking at the hook up to drain I realized the tub also has a below floor trap. Maybe it always froze but the tub hadn't been used during those periods.
(house not occupied full time the past few years but we did use the laundry which is how i found the frozen trap problem when the laundry room and kitchen floor flooded LOL)

How do you keep a trap from freezing in this situation?

the insulation wrapped blob to the right of the trap is the waterlines coming up out of the ground.
I've struggled keeping that thawed also. Now have a heat tape and wrapped with r13 and so far so good at least last winter.

I think they say don't put heat tape on pvc, not sure.
maybe if i wrapped it in R30???
or have people pour antifreeze down drain after every shower?

the only heat tape I would consider is 'frostex'.

it is self regulating so it requires no thermostat.

look it up.
[www.nventthermal.com]

also do a perimeter insulating all around the crawl space. I see bricks in your picture.

\put 2 inch Styrofoam all around and toss some dirt along the bottom of it. keep the cold out..

if the layout allows, create a little 'room' around the trap location with Styrofoam.

great! thanks for those suggestions...sounds good