My 20,000 gallon plaster pool was recently refinished by our pool guy, and he filled in the main drain because he said it was leaking and couldn't be fixed. I have since taken over the pool and maintain it myself, and am trying to figure out the main drain issue. There are two 1.5" pipes teed in to the inlet side of the pump, and if I shut off the valve on one, nothing happens, shutting off the valve on the other starves the pump. This is consistent with the main drain being plugged up. I dove down and removed the cover from the drain to vacuum out some crud that had collected in there, and found that there were two 1.5" pipes plumbed in to the drain. One appeared to have gone straight down, and is packed full of concrete, this must be the one he blocked due to the supposed leak. Then there is one that appears to run horizontal rather than straight down. I was able to push a screwdriver in about 10" without feeling any resistance or cap. Any idea what this could be? Is there a chance two lines were plumbed to the drain? I have heard of this being done, but couldn't find it anywhere near the pump pad.