Magnesium sulfate / potassium sulfate / sodium sulfate
"What's worse than having to take this stuff?  Having to take the second dose!!!!  I got 3/4 of the second dose down before intense gagging.  NEVER AGAIN!!!!!!  The taste is like disgusting grape cough medicine.  After starving all day, the overfull feeling of this plus the extra water you have to drink in the hour is terrible."