I have done so many flushes in last 12 years with Dr. Clark and Dr. Sutter protocols. I also have had big stones, 1" + many times with no pain. As the other two posters mentioned ES is the key.
However, if you want to be sure that you have huge stones, get a sonogram done of your GB. Also besides malic acid, you can include Gold Cion Grass and Tirmeric to break up the stones.