As others have said the water can get a bit yucky. There are 2 main ways to empty the water out if there is not a plug. The easiest is to siphon, and let the water run onto your plants. The other way is to scoop it out. Again you can put the water onto your plants or down the toilet if you prefer.
To protect your floor a couple of shower curtains from the cheap shop works well. Put the shower curtains on the floor, pool on top of the curtains and a few old towels on top of the shower curtains around the outside of the pool.