I am having some repairs done on a return line, so the pool company plumber went ahead and did the closing for me today. I noticed that he blew out the main drain line at the shutoff valve junction near the pump. He then added antifreeze to the line, re-attached the shutoff valve and called it good. I questioned him about the lack of an air lock and he said that was not necessary due to the depth of the main drain line. This seems odd to me since all previous closings have used the airlock approach - any input on this?