I wonder if it’s possible to fast for a certain number of days, and then take a mild laxative or even no laxative at all?
Not a clue, but I found that my Doc was very thorough about explaining exactly why he needed this specific set of procedures. I'd give yours a call and see what he or she says.
Without being overly graphic, I did get to see that "empty" isn't entirely empty, which is about what you'd expect in the plumbing biz.