*wonders if Johnny tried the experiment with the ziplock bag*
I never liked waterbeds the few times I've slept on them, so I never got one and don't know much about moving them or filling them properly but I do know Vask is right about the water/weight and there's a LOT of water in a king size waterbed! So yah, draining it at least part way is about the only way you'll move anything that heavy/big!
My husband and I are shopping for a new bed and he used to have a waterbed and loved it, but we decided to go with a conventional one for several reasons but mostly we didn't want to worry about all that water if it should spring a leak!