I just looked up the ingredients for Colonix and there doesn't seem to be any senna or cascara sagrada herbal laxatives in there, so that's good! (you don't want to have herbal laxatives because they don't strengthen your own muscles - peristalsis - they irritate the colon and that's how the fecal matter passes)
Looks like if you've been drawn to that products that might be the one for you!
Eventually, you might just want to do the simple Bentonite and psyllium (for your 3 week yearly bowel cleanses?) as it's cheaper and pretty simple. Bentonite draws the toxins to it and the psyllium sweeps out your intestines...I've gotten big old ropes from this stuff!
So...for the future, you might want to read the link below about b&p's.
Oh yeah and if you're interested in fasting...you can check out thise link: http://www.geocities.com/HotSprings/Spa/7244/master_cleanse.html and click on 'recommended messages' in the Fasting Forum Archives and Active! (a quick way to read the most inspirational messages)