Only fat floats on the surface of water.

When the phrase "healthy stools float" goes around it's a misquote. It means that ideally, they shouldn't be so totally heavy with gunk that they sink and crash to the bottom of the bowl. ;) They should sink slowly and maybe not rest entirely on the bottom, but that depends on many factors in your diet and colon.

Mostly you want to check for color and thickness and whether it's totally compact or not. Healthy stools are medium to dark brown, and should be formed but not compacted, and very thick and long, unless you ate something that moves quickly thru the colon.

Hope that helps! :)