I have done many flushes without the preparations. The Master Cleanse will help cleanse your kidneys and bowels. I have had some wonderful flushes after doing the Master Cleanse. One thing I advise though is to try and drink diluted apple juice for two or three days before you flush. The oil used in the flush is heavy and can be quite a shock to the system. The heavier sweeter apple juice will help prepare you for the flush and lessen the chances of throwing up the oil and grapefruit juice. Also use apple juice for taking the Epsom salt, it makes it go down much easier. Sucking on a lemon or lime after the Epsom Salt also helps quell the taste.
Several of us have done Liver Flushes after MC, feel free to ask all the questions you want.