You will not get the "runs" on the Master-Cleanse necessarily, unless you do the salt water flush. If you are cleansing to get the gunk out of your colon this is well worth learning to do (it does not come naturally)!
It only took me four years to figure out there is an easier way:
Dissolve 2 tsp. UNIODIZED Sea Salt (available at health and gourmet stores) in ONE cup drinkably hot water.
Have THREE cups plain water standing by.
Chug as much salt water as you can, and chase with fresh. Chug and chase til ALL water is consumed. VOILA! In 1-2 hours the entire quart will exit south, carrying mucho gunk with it. Not recommended for the commute!
Even if you only do this a few times while MCing, you will find it extremely productive.