How to determine when your colon/intestines are clean?

Bowel Purge: The absence of solid fecal matter as well as light yellow or clear liquid output from the bowels would suggest clean or cleared intestines. Many agents are used to purge the bowel prior to colonoscopy and the endoscopist looks for the aforementioned to determine the quality of the bowel preparation. Bear in mind that by definition, the bowel is not “clean” as it is full of normal bacterial flora.