Magnesium sulfate / potassium sulfate / sodium sulfate
"I'm in the middle of the process right now!  I didn't find the taste all that unpleasant.  I drank it all at the same time which MIGHT have been a mistake because I then had trouble drinking the additional water (but I DID drink it).  I just figured it would be best to get it all down in one shot.  It began working in around 30 minutes and I've already gone to the bathroom at least six times.  With each bathroom trip, everything is lighter in color and clearer which I suppose is the goal.  I'm just now feeling that I won't be going much longer...it has been 1 hour and 45 mins since I started the prep.  I've not experienced pain or nausea.  Although I admit I'm not looking forward to doing this again tomorrow morning.  :)"