Really there should be no air. If there is, it is coming from somewhere. I have seen lids with micro-cracks in the plastic that leak. You can sometimes test for this but running water slowly over the top while seeing if the air goes away or put some plastic over the lid. Also with lids the o-ring is always a suspect. From time to time you will get air that makes its way from your returns/skimmers but this should usually work its way out of the pump basket. No matter how much air is in my basket, if I turn the pump to full speed, it will quickly disappear.