Have you try your local American Leak Detection company?
http://www.americanleakdetection.com/
My pool was losing 1 inch per day after I drain and refill it.
BTW, that is what I get for completely drain the vinyl pool.
Don't do that.
My local American Leak Detection company quote me flat rate $375 for detect and fix
the leak up to 5 patches, including fixture like drain and skimmer. I am not
sure about the pipe though.
Any way. The local owner comes to service my pool today. He find
two holes right away, using some specialized electronic gear.
I am very impressed. I have been using food coloring in
that area and I did not find it. The bigger hole is obvious once I know
where to put the color. The smaller one is impossible for me to find
by myself. It is barely drawing food coloring even if I know where
to look.
I was suspecting the drain. It turn out the drain is fine. He has some
specialized tools to test it as well. Very clever.
I was charged $275, less than the quote price because no
diving is required. I am very happy.