I have done many flushes in my life. I can assure you that nothing is wrong with cleaning the colon with Mg-Citrate. If you want to be 100% sure, you can do an enema.
I have never done any other Colon Cleanses before and after the flush, but what is in Dr. Clark's protocol.
I don't mind Vitamin C flush. You take 5000mg of Ascorbic Acid in warm water, if you do not get any diarrhea then take 1000mg more, then more if needed.