I've already replaced the o-ring on the pump basket lid and drain plug, and greased both of them. I've tried pouring water over the different joints b/n the ground and the filter and haven't been able to tell a difference. When the pump is running it holds prime and I don't really see any air in the pump basket, maybe a few small bubbles once in awhile. But my sand filter has a clear dome on the top and I can watch the air bubbles streaming to the top and the water level dropping. It happens pretty quickly. If I release all the air and then turn off the pump, a small amount of air bubbles into the pump basket but it stays full of water. The water level in the filter starts dropping immediately and I don't see any noticeable leaks in the connections.
Any ideas on what to look at next?