Wow. Special thanks should go to StagnantReaction, Gary Gnu, and Jdude3 for giving real information, and for questioning this ridiculous idea of a "colon-cleansing."
I cannot believe that people are buying into this. Colon-cleansing is a marketing niche that preys on people's paranoia and disgust over their own bodily functions. They tell you that there is "5-10 pounds of rotting feces sitting in your colon" and then of course people think, "wow, thats disgusting, I better buy this product." It's complete bullshit, do not ever buy any product claiming to clean the colon, and do not ever get an enema unless medically necessary.
The human body has evolved over millions of years and it works very well. If left alone, and provided with enough fiber, your GI tract will keep itself quite clean. Feces does not build up in the colon unless you allow it to, or you have a blockage caused by a tumor or a foreign object. If you get constipated, eat more fiber and make sure to drink enough water.
If you are really paranoid, try fasting for a day or two. Your colon will be spotless after that.
But be realistic people! Your GI system processes food and then turns it into feces. For some reason, to certain weird people, this is offensive and they want to "clean out" their system. It's essentially the same thing as people who cannot stop washing their hands or swilling mouthwash.
STOP IT! Your body works the way it does for a reason...and you screwing with it is not going to make it work better. The lack of physiological knowledge here is a problem.
Please realize that colon-cleansing is a snake oil product that is targeted at people who are obsessed with their own bodily functions. While it may help a small number of people with an actual GI problem, the vast majority do not need to have their colon cleaned out.