It's entirely up to you how long you should wait. The reason Dr. Clark says to wait about three weeks in between flushes is because it gives the stones that were in the back time to move forward. But, everyone is different. Always keep that in mind. What may be right for one person may not be right for another one. So, you do what you want. I have read where some people have done their flushes weekly and gotten good results. Then some just do one flush and that's it. Personally, I don't understand doing just one flush because there's no way you can remove all the stones!