Colemas fall somewhere in between an enema and a colonic. The standard enema bag holds 2 qts and most folks can't get beyond the sigmoid...never beyond the descending colon. Colemas usually use a 5 gallon container...you can get further...but still not as far as a colonic...which can clear all the way to the cecum. Actually, an open-system colonic is not much more than a colema...they may use more water...but the dynamics of it probably still won't let you clear out the entire colon. Although it is a significant expense up front...if you really want to splurge you can get a home colonic unit that comes pretty close to a professional closed-system colonic...the Colonet Jr. I'm not sure of the link, but I think it will come up if you run a search.
Too bad you're not near Chicago...I fix you colon good!!! ; )