So we have had two nights at about 0 degrees. I did remove the waterline and used tank water. I have a commercial heat tape on the waterline with foam insulation on top of it. When I bout 6” plastic ductwork for my underbelly furnace install I hade extra 6” ductwork. So i installed it over top of the waterline for two reasons. More insulation and just in case we needed to travel. I could just pull it out if the 6” is frozen in place..
Now I did try to seal the end so as to stop water infiltrating the fiberglass.
Vern in a T-shirt