What’s the problem? You get the mattress to he hallow end. Lift a bit out of the water, wait for it to drain. If the edge of the pool ois too rough (concrete, not tile) use a tarp or plasic to make it slide. Get a few inches out, let it drain, a few more inches, etc. It will be a long process, but doable.
A mattress underwater is as heavy as dry out of the water; in fact lighter, by the volume of water that the cotton/polyester/metal springs/whatever displaces. Tilt, push the low end so the other end pokes out of the water. A damp but drain mattress is not that much heavier, and you are sliding it out of the pool a bt at a time, not lifting the whole thing.
If you include the water trapped inside the mattress, then a wet mattress is heavier than a dry mattress, sitting on land out of the water.
However, if you consider the situation of a saturated mattress submerged under water, then the water in the mattress is now neutrally buoyant, and therefore does not contribute to the apparent weight of the mattress underwater.
And because of the force of buoyancy, the apparent weight of the submerged mattress is less than that of the dry mattress on land. Q.E.D.
Side note: when I wrote my quoted post above back in 2005, I was just four years removed from having taught this material in a physics class. I’m definitely feeling far more rusty six years later, a full decade removed from teaching.
That being said, I believe that I should have used the term “apparent weight” in my earlier posting, that is, weight (mg) as offset by buoyancy (B).
