I'm looking for advice from someone with experience doing an air lock on the main drain. I am doing this when I close this year. My pool has the main drain line coming from the bottom of the pool into the skimmer. I installed the proper plug in the skimmer and then let the compressor rise to about 60-80 lbs of pressure. I then put air in the line and waited until I saw bubbles coming from the main drain (which took about 10-15 seconds). After I started seeing bubbles I continued putting air in the line for about 20-30 seconds. Does that sound about right?