Since this is also my first experience with liver cleansing, I am not sure if I can help you much, but I will try. I know that if you do a Liver Flush and your stools are still grayish in color, then that means you have a stuck stone. Usually for that, you should drink some apple cider vinegar (I drank about a tbsp a day and now I have some mild pressure in my right side so I am going to start doing some actually flushing pretty soon. I think the pressure it probably coming from a stuck stone). The ACV will help to break up the stones a bit to make them easier to pass. I've heard that you should drink it a week before flushing. One thing I will warn you of ...you may want to drink it in small amounts because if you already have too much stomach acid as it is, then it's going to give you heartburn.
Anyways, good luck with flushing! :) If you want to know anything else about it, Shelly has a great FAQ on it (look at the "best of Shelly" link at the top) and CureZone's main page has a link to Liver Flushing and the different types you can do. Try experimenting with some and see which works for you!