Thought this might be of interest. I apparently have had for some time now a hole somewhere in the bottom of my in ground pool. The result was that the liner floated, like it had a large air pocket. This pocket was about 10 x 10 foot. You could move it around by walking on it but eventually it would return to it's original location. I put on a mask and snorkel but could not find the hole. I finally broke out my dive gear and found the hole in a crease in the deepest part of the pool, about 6'6". I got on line and found a couple of post at different websites but nothing that looked promising. One person suggested greasing up a small plastic tube and pushing it down from the liner top. Well, I bought all the tubing a small pump and a tube of lithium grease...believe me...I tried everything I could but could push the hose no more than about 18" and then the liner would squeeze it so tight that it would go no further.
Then I thought that I would try to take the vacuum hose from the skimmer down and put it over the hole....the hole was about 3/4" and sort of ragged. Sure enough it started to suck out the water from behind the liner. I had a pool patch kit and after the water was gone, I tried to patch the hole, since it was in a big crease it was a no go....man was I disappointed. The liner was looking good, the water was gone but I couldn't patch the hole.
Back on the internet to see if I could find anything that would patch it under water...and this is the reason for the post. I found a product called Flexible Sealer Permanent Bond All Purpose Sealant. The name was Leakmaster by Anderson. Well, I bought two tubes and it comes in white or blue. The directions are pretty straight forward, but in a nut shell when it comes out of the tube it's like a soft blue bubble gum. I reattached the hose and sucked out the water a second time. The with dive gear on I went to work on the hole. You mold it with your finger tips and you can actually fill in the hole, layer it and shape it any way you want. I covered both sides of the crease then filled in the hole. Worked like a charm. That was a week ago, I've since gone down and checked, no leak, no water behind the liner. Hope this helps someone who has a difficult patch to make on a vinyl liner pool.