It is VERY important that before anyone does flushes etc, that their eliminitory organs are working well so that they are able to handle the toxins and flush them out.
It is usually recommended to do bowel cleansing first and then a Liver/Gallbladder Flush and then Kidney, and then Blood Cleansing.
I have done The Master Cleanse for 38 days before, and many times before that, and I now wish I hadn't and stuck to juice fasting, this way for sure you are getting all of the nutrition and protection during the process.
What I strongly suggest is making sure that everyone drinks a potassium broth on a regular basis to make sure they are replacing the vital nutrients... that they loose from fasting, flushing, cleansing...
It is also highly recommended to do an enema before and after these things, and for fasting; before, during and after.