I've got one particular pipe that I'm concerned about. It runs from the filter output (high point), then turns down and runs along the slab, then turns back up as it enters the heater (high point). The booster pump taps into that pipe as well, as you can see. Even when all the water runs back into the pool from most of the pipes, it seems to me like this one pipe will remain practically full of water and would be a serious freezing hazard. Thoughts? Previous owners supposedly ran the pump 24x7x365, so this wasn't an issue.
I might could Shop-Vac enough of the water out, but I'd have to disconnect and move the filter. Maybe install a T with threaded plug in the horizontal section of pipe running along the slab?