My wonderful naturopath has me wait until digestion has fully reestablished after fasting to flush my liver . The Master-Cleanse is a good kidney flush, but if you are concerned, consider drinking Watermelon Tea as part of your fast. Roughly chop 1 T. Watermelon seeds. Cover with one pint boiling water and allow to cool. Drink as your daily water intake while doing the MC! This is an excellent kidney cleanser.
If you have the luxury of a professional colonic, do it AFTER the Liver Flush to make sure you've gotten all the gunk you've flushed out! Great thing to do! And a nice follow up to the MC.