Summarize this article:

Start by removing all bedding from the waterbed. This includes removing mattress pads, sheets, comforters, pillows, and everything else. Ultimately, you won't be able to drain the bed without stripping it. After stripping your bed, take a few towels and place them around the waterbed. You may also want to position a few around the ends of the waterbed mattress so they can catch any water that spills. Keep extra towels around in case you have a spill larger than you anticipated. Go behind the bed and unplug the waterbed heater and any other plugs that might power some aspect of the bed. Without unplugging the waterbed, you could damage it or put yourself in danger. The fill-and-drain valve is the valve you use to fill or empty your waterbed. This valve is very often located toward the foot of the bed. It may be in the center, or it may be toward one side. After you find the valve, remove the cap from it. Push out as much air as you can from the mattress. Take a light broom and sweep from the top end of the mattress toward the valve. Remove as much air as you can, as air will slow down and complicate draining the bed. By placing the cap back on the valve, you'll stop air from getting back into the mattress. Make sure you tighten the cap so water doesn't get out, either.

Summary:
Strip your bed. Place towels at the foot of your bed. Unplug the waterbed. Find the fill-and-drain valve. Empty extra air from the mattress. Place the cap back on the valve.