I just start using one recently; basically these are tanks with water that is heated to body tempature.. and filled with 800lbs of epson salt so that you're body floats right on top.

In complete darkness.. this eleminates external sensory input. So far I haven't been tired enough going in.. but I will post if I have success WILDing in these.

There's some more information at www.floatdreams.com and www.floatation.com