If you have UC, don't do it. I met a girl on Remicade that said she got it done to lose weight and she swears that was what triggered it to start. I wouldn't mess with it, healthy or not.
Colonic irrigation can potentially cause severe adverse effects and must be carefully administered. People receiving frequent treatments may absorb too much water, leading to electrolyte imbalances in the blood, nausea, vomiting, heart failure, fluid in the lungs, abnormal heart rhythms or coma. Infections have been reported, possibly because of contaminated equipment or as a result of clearing out normal colon bacteria. There is a risk of bowel perforation (breakage of the bowel wall), which is a severe complication. Deaths have been reported.
Colonic irrigation should not be used in people with diverticulitis, ulcerative colitis, Crohn's disease, severe or internal hemorrhoids or tumors in the rectum or colon. It also should not be used soon after bowel surgery (unless directed by your health care provider). Regular treatments should be avoided by people with heart disease or kidney disease (renal insufficiency). Be sure that the equipment used is sterile and that the practitioner is experienced. Colonic irrigation should not be used as the sole treatment (instead of more proven therapies) for severe conditions, and it should not delay consultation with a qualified health care provider for a potentially severe symptom or illness.