How do you fix a crater under the pool liner?

I havew an inground vinyl liner pool that got water behind it from a leak. The walls started to bulge from all the water behind it. I was afraid I would need to drain the pool to fix the problem. But I was told to just use a shop vac and suck it out. What I ended up using was a submersible sump pump, and a garden hose. I ran the water back into the pool, and it seemed to work. You will need to pop off some of the beading to get the draining equipment of choice behind it. It isn't too dificult, and much cheaper than hiring a pro. BUT BEWARE make sure the equipment is out beofre the vinyl is sucked back to the wall, other wise you will need to find a way to remove it a very tight liner against it. (sound like advice from experience?) good luck!