A shop vac can be used to clean a pool. They are different from your regular vacuums as they can suck up liquids, which makes them good cleaning equipment for pools. They however need to be adjusted for vacuuming water first.
All you need is a medium-size water or vacuum pump. Unroll the pump's intake hose so that it reaches the center of the pool (or as close to it as possible), and submerge it in the pool. Place the outlet hose so the exiting water doesn't flood the area, but drains off away from the pool.
If there has been a serious invasion of excess dirt and debris, you may also need to shock your pool. Vacuuming is recognized as the only way to remove sediment from the bottom of a pool.
If ground water is not a problem a pool can be left empty for weeks or even months as long the hydrostatic relief in the bottom of the pool is open and functioning. If the time frame of the pool being empty gets into freezing weather there is real risk of freeze-thaw damage to surface of the pool.
You'll need to keep draining water off the cover with a pump or siphon to protect it from damage. Important: Never drain an above ground pool completely when winterizing. Your vinyl liner can dry out, shortening its life considerably.
As noted, typical maintenance or winterizing your pool shouldn't require you to completely drain the water. You risk damaging your pool liner and the structure of your above ground pool.
Even with proper and regular pool maintenance, it's often necessary to drain your pool — completely or partially — every 3-5 years. Draining your pool often isn't necessary, especially if you're following a proper and regular maintenance program.
First, if the draining is done at the wrong time or under the wrong conditions, you can actually risk damaging your pool structure and liner. All the water from your pool needs to go somewhere when it's drained, and that usually means the ground.
Much of this rain water penetrates into the ground, raising the inground water table, which creates a lot of hydrostatic pressure pushing up on the pool. After the water table raises enough, the pool may float or pop up out of the ground.
Vinyl pools tend to contract when emptied, which can result in damage when they are refilled. Gunite or fiberglass pools can crack, and fiberglass pools may suffer bulging or splitting if drained.