Dr. Clark recommends a parasite cleanse followed by a liver flush - some people say do a flush after a parasite cleanse. I personally do one before a parasite cleanse to get the ducts cleaned out and the bile flowing good. The parasite cleanse needs a good functioning liver to help detox the body. I then do one afterwards to just to be on the safe side.
A liver flush is not required in order to do a parasite cleanse, but if you're in the cleansing mood - why not go ahead and get it all done at one time.