The claim is that the 'plaque' lining the bowel can't be sloughed off in one go and needs a few trips to get rid of (at �50 a pop, no wonder they recommend this!).
Truth is the gut is a finely tuned and well-functioning organ that doesn't need any help to get clean. If you are concerned, try pysllium husks instead (which colonic therapists recommend before a 'flush' to clear out the cr@p!). They bulk up in your gut and push out any poo that shouldn't be lingering around and slough out your gut in a safe and healthy way without the need to stick a pipe up your bottom! You can buy them at any health food shop - just mix with water first.