I've been looking over some closing posts and have a couple of questions I don't see addressed.
1. I understand the line blowing concept for the skimmer and jets, but what about the main drain line? I also have an in floor cleaning system which has three pivoting pop ups in the floor, which would need the same attention as the main drain line I think.
2. I understand the concept of the "frostline" underground about 18" or so (being a constant 54 degrees or so), but what is the effect of the frostline in the gravel pit around the pool? It's about 4 feet under the surface, but not in the soil/earth. This is where I'm concerned about the water standing in the main drain and pop up lines.
Usually I pay the pool company to close the pool,they pump anti freeze through all of the lines, and boy is it expensive, almost $500, this uses 43 gallons of anti freeze at $5/gal. and a hefty labor charge-and they're only here for 25 minutes.