Magnesium citrate
"Make sure you drink more than 8 ozs of water after taking the whole bottle.  LOTS OF WATER right after taking it..  You will need butt ointment, vinyl gloves, baby wipes, and garbage bags.  I had to take 3 bottles in 24 hrs  for the colonoscopy.  My butt was terribly raw,  I used cold pressed castor oil, but I heard A&D ointment works good and prob won't be as oily..  It took 2 hrs to work with just 8 ozs of water, but would have worked sooner if I had taken 16 ozs of water.  The more water you drink the more it will work.  I bought lemon flavor at Big Lots, but I've heard it comes in grape or cherry."