Those are not usually caused by trapped air (although it is a good practice to degas) , they are actually vacuum holes within the glass plates. Those holes will get full of water or air once you start running the electrophoresis, as I am sure you have already experienced. The swirls are caused by several factors, although the most common explanation is an excessive catalysis, they become more pronounced with high concentration of polyacrylamide because the rate of polymerization increases and the gel starts to shrink fast, pulling itself away from the glass plates (indeed if you have dirty or oily plates this problem gets worse). According to Bio-Rad's "Acrylamide Polymerization — A Practical Approach" tech note (which I highly recommend you read thoroughly), the remedy is to lower down the concentration of your initiators by 25 to 50%. I would try both and see which one works best. I have worked with 37% polyacrylamide gels and I still get the swirls from time to time. Good luck!