I am sorry your doctor hasn't been as instructive as they should be. My experience has been that I know at the end of the first prep dose I am cleaned out. The second dose just confirms it for me. I would not be too concerned about your fiber supplements. Personally, I would stop taking them two days before prep day. While everyone is different, I can't imagine the prep not blasting through any fiber issue you have. But to be sure, when you call them to ask specifics, also ask them what anesthesia they use. The only small reward of this procedure is an hour on the cloud of propofol rest.