As a general rule, once a liner is installed, the pool should never be drained. You may get away with it in the first few years but after that, the liner starts to lose its elasticity and you run the risk on the liner ripping or tearing when you try to refill the pool. This is the same problem you encounter if the liner has floated and needs to be reseated. Our advice would be to always clean a pool while still full of water. Fish out the big debris and then let the filter and the chemicals do their job. If it’s just dirty, the chlorine will burn up the organic stains, given time. If you have metallic stains, click here to see our previous post on how to identify and address those.