Magnesium sulfate / potassium sulfate / sodium sulfate
"First time colonoscopy.  Took first dose at 2pm with a lemon wedge chaser to kill the anticipated aftertaste then 32oz of water quickly thereafter.  Most taste was gone after the lemon juice.  It's a lot of fluid to drink at once but not that bad. 15 min later I was off to the toilet...off and on for the next 11/2 hrs (not stuck on toilet for the entire time though) this stuff really works.  Next dose at 8pm, with the same result as the first time.  I was able to go to bed at 11pm with no further effects.  Got up at 6am feeling good for my 8am procedure.  Doctor said the prep worked well.  I tolerated this bowel prep pretty well and didn't suffer any side effects other than the urge to go."