Good news! MY son came over to pick up my granddaughters and he went out to the sand filter and literally laid down on his belly to look underneath. It was the drain plug after all. He said I would never see it standing up or kneeling. Even though I ran my fingers along the shaft of the plug, I did not feel the water. He said water was actually trickling down from out the bottom of the plug, running underneath the bottom of the filter and coming out from under the filter "stand", making it look like there was a possible crack in the bottom of the filter. While he was down there, he also found the round "gasket" from the drain plug laying in the gravel. He put the gasket in, screwed it back on and no more leak. I should have been more persistent. I can now smile as I won't be calling my $350.00 hr pool people. Thanks to all of your for your wonderful help. Without this website, I would not be enjoying my beautiful sparkling pool, nor would I be able to do the opening and closing by myself.