When completely full of water, a waterbed mattress becomes extremely heavy. If you are moving or replacing the bed, you will need to drain it. The most convenient way to drain a waterbed is with a waterbed drain kit, which includes an electric pump to siphon water out of the mattress. However, if you do not have waterbed drain kit, you can use gravity combined with a garden hose to drain it.
Unplug the heating element of your waterbed if it has one.
Extend a garden hose from the waterbed to an outside spigot. If the garden hose won't reach, combine multiple hoses. When combining hoses, ensure that the connection is sealed tightly. The spigot must be in an area that will allow the hose to fall to a lower altitude than the bed, otherwise, gravity will not drain it.
Connect the garden hose to the spigot.
Screw the waterbed drain connector onto the other end of the garden hose. A drain connector should have been included with your waterbed. If not, waterbed drain connectors are available at hardware stores.
Pull the waterbed fill tube up so that it no longer is pushed into the bed. Unscrew the cap, then remove the pull cap.
Gently "burp" the bed to remove air pockets by running a broomstick flat against the top of the mattress towards the valve.
Insert the drain connector into the waterbed valve, then screw it onto the valve.
Push the waterbed fill tube back into the bed so that the opening is level with the mattress.
Turn on the spigot for about 15 seconds to run water into the bed, eliminating any air bubbles within the hose.
Turn off the water, then remove the garden hose from the spigot, allowing it to fall to the ground. Once removed, the water will be siphoned out of the waterbed.