Polyethylene glycol 3350 with electrolytes
"My 81 yr old father had to get two colonoscopies in 3 months.  For the first one, he used a different prep that required him to drink a gallon of liquid.  He had a really hard time with it and didn't finish it.  The main advantage of Moviprep was that it is much less liquid.  We mixed it up the night before and put it in a refrigerator set low so it would be very cold when he drank it.  We also mixed a little lemon-lime Vitamin Water, made him use a straw to drink it, and had him suck on butterscotch candies after each drink and he got through it all pretty easily.  I can't rate this a 10, since it still doesn't taste great, but it was much better than the other stuff he had to drink."