Magnesium sulfate / potassium sulfate / sodium sulfate
"As a general rule I don't like liquid medicines, however I did find a few tricks I have read on the internet worked quite well for me and maybe for some other people with issues.  I found that putting the prep bottles in the fridge for about 12-24 hours before use so as to make the solution as cold as possible makes it taste less like medicine.  I also found that reconstituting the Suprep with ginger ale instead of tap water helps to get the prep down much easier.  Also use a straw so that you can shoot the medicine as far back in your throat as possible to avoid as much as possible certainly helps."