Our 20x40 in ground pool seems to have 2 main drains. One is in the shallow end (4ft) and one on the deep end (10ft). I am not sure if both of them are called "main drain". While blowing the lines during closing (in NJ) we saw bubbles/water moving on top where the drain is in shallow end but we never saw any water moving on top of the drain in the deep end. We used air compressor and waited 15 minutes, nothing.
Should we be worried? We didn't use any antifreeze, should we?