I have a 2 year old Pentair SD 80 sand filter that is leaking somewhere out of the bottom. I can't see exactly where because the stand that it sits on is in the way. There are only two openings on this unit. The drain at the bottom and the opening at the top for the multi-port valve. The water is not coming from either of these. To add to the mystery, at times it appears as a steady stream (not a river, but definitely steady) and then at other times I don't see any water at all! Has anybody else experienced anything similar to this?