would do The Master Cleanse first and finish with the liver flush. The Master Cleanse helps the body to dump a lot of toxins, cellular debris, etc.. So finishing off a Master Cleanse with a Liver Flush helps sweep debris from the liver that has accumulated from the cleanse. Also, since you aren't eating any fat on the MC, you should build up some back pressure of bile which will help with flushing the liver.
Actually, if you wanted, you could do a Liver-Flush before The Master Cleanse also, just make sure you time it so you have at least 2 weeks between the flushes so you can build up the bile salt pool for the second flush.