The only thing I will disagree with FGM about is that there are some medical uses for enemas. For example, in cases of extreme constipation, before colon surgery, a colonoscopy, or other procedure, and sometimes to women in labor (so they don't poo on the table).
Everything else, FGM is totally right. Your digestive system is very very efficient. All that stuff about toxins building up is a lot of hooey. It's something they used to believe in the 1800s, and some people still believe it, for some reason. It is also no more of a weight-loss technique than going to the bathroom normally.
There are risks to using enemas, such as dehydration (with over-use), rectal bleeding, and colon perforation; these aren't common, but are very serious when they do occur. Certain types of enemas have been known to cause death (with coffee enemas) and inflammatory bowel disease (ozone water enemas).
If you want to keep things...moving, eat a diet high in insoluble fiber--it's nature's broom!