That is one of the reasons that you take the Epsom Salts - not only to relax the bile ducts, but also to clear the colon. Clearing the colon before drinking the olive oil mixture is an important part of the flush. It allows for a better flush because there are no obstructions in the colon and also helps prevent nausea and vomiting.
I have done protocols for a lv/gb flush that did not use Epsom Salts or clearing the colon before hand and gotten very, very sick - and have known others who experienced the same when not taking the ES or not taking enough. If you have diarrhea and clear out before you drink the oo mixture - you are right on track!
Sometimes too, the Epsom Salts relax the bile ducts so much that you flush out built up bile and sandy crud before you drink the oo mixture and that's a good part of what you are expelling. This, once again, is a good thing. It means when you drink the oo mixture you will be getting out more stones.
Don't ever 'fight' the diarrhea - if you have the urge to purge - let it go or you run the risk of recirculating crap through your system and are defeating the purpose of the cleanse.