the question came up after seeing this:
https://postimg.org/image/243f02yniz/
seeing all the negative feedback, i’m under the impression that ‘no’ - they don’t work
Funny story…had a waterbed on the 2nd story of a house I rented with some friends. I needed to empty it to move it to the other side of the room, so had one buddy downstairs with the other end of the hose, performing the aforementioned “sucking” procedure but nothing coming through until I proceeded to put some weight down on the bed. Needless to say, he got a mouthful he hasn’t forgotten.
I miss that bed too.
FWIW there’s some evidence that waterbeds can help prevent bed sores.