Colonic irrigation. Patient undergoing colonic irrigation, or colon hydrotherapy. This is a form of alternative therapy whereby the colon (part of the large intestine) is flushed out with water or another liquid, introduced through a tube inserted in the person's anus. It is said to improve the health of the patient by removing harmful bacteria, toxins and waste said to line the walls of the large intestine. The scientific basis for the alleged benefits of such a procedure are debatable.