Don’t drain a vinyl liner pool!
The most important #1 rule for vinyl liner swimming pools is do not ever, under any circumstance, (except replacement) drain the pool. I cannot stress this enough. No matter what problem you are attempting to fix, DON’T DRAIN IT! The only time it is ok to empty a vinyl liner swimming pool, is right before a new pool liner is to be installed.
I have had people come into my store and tell me they’ve drained their pool and their looking for something to clean the liner. This is the point where I have to tell them that the liner probably needs to be replaced. When a swimming pool liner is installed, the weight of the water stretches the liner into place. That vinyl is made to hold that same position until it needs to be replaced some 15 or 20 years down the line. When the water is removed from the pool, it shrinks back smaller then when it was new, or if the liner is older or brittle it may shrink only a little because it has lost its elasticity. Now that the liner has been stretched and contracted, when it is refilled it will probably rip. Usually a seam will separate or the swimming pool liner will tear away from a skimmer or inlet. At this point a new liner is needed.
I could write for hours about this subject and give dozens of examples that I have seen over the years. I’m not going to do that. I’m going to make it very simple and very clear. If you are not replacing your liner or do not want to have too, NEVER DRAIN A VINYL LINER SWIMMING POOL!!