I think the clay is supposed to draw out impurities. Same principle as a clay mask for your face -- at least, that is what I have been told -- though a different kind of clay is used, called bentonite.
"Bentonite clay, a medicinal powdered clay which is also known as montmorillonite, derives from deposits of weathered volcanic ash. It is one of the most effective natural intestinal detoxifying agents available and has been recognized as such for centuries by native peoples around the world. Whatever the name, liquid clay contains minerals that, once inside the gastrointestinal tract, are able to absorb toxins and deliver mineral nutrients to an impressive degree, says Knishinsky. Liquid clay is inert which means it passes through the body undigested."http://www.experiencefestival.com/i/...s/article/2064
Bentonite is what my co-worker used. She felt like it was doing her some good, but she was always taking something for her colon and talking about her poop, so it was kind of hard to tell whether it had real benefits or was just part of her obsession.