I am trying to figure out if blowing out the water in our main drain pipe in our inground pool is really necessary. Our pool is 10 feet deep in the deep end and water would never freeze at that depth even with our harsh winters here in Northern Ontario (Canada).
Our neighbour has had a pool for more than 30 years. It is an inground vinyl pool with a 8' deep end. He has NEVER done anything related to the main drain when winterizing/closing his pool and has never had any issues. He does clear water from the return and skimmer lines (but does not use antifreeze). He helped us close our pool last fall and so we did nothing to the main drain (didn't occur to me that there was even a way to do that) and it was fine. When we opened the pool in the spring we had a very difficult time getting water back into the pipes (including the main drain) and priming the pump. This suggests to me that there was a lot of air in the main drain pipe even without taking any action to clear it.
Also, my thought was that if the water does not freeze at that depth, and the drain at the bottom of the pool is open (which it always is), if water did start to freeze in the main drain pipes, wouldn't it push water back into the pool. In other words if some ice formed, it would not form down to a ten foot depth and therefore any pressure caused by expanding ice would just push the water that was not frozen back into the pool. If you leave the valve for the main drain (near the pump) open, that would give additional room for freezing water to go to.
There may be an obvious flaw in my logic that I am missing. Would appreciate hearing others perspectives on this.