I use Golytely (sp?). I usually ask for a citrus flavor to add - lemon, lemon-lime, etc. I've heard you should avoid any cherry or berry flavorings. As some have already mentioned, chilling it helps and drinking through a straw helps. I can never get the entire gallon down - but by the time I finally throw up the white flag, I'm basically pooping clear yellowish liquid. My surgeon said so long as I'm not shooting out chunks (sorry - kind of graphic); that's her main concern. So liquid, clearish, no chunks - all good. I usually make it about 2/3 of the way through the swill.
I don't just randomly decide to stop drinking it. If I don't finish it off it's because I KNOW my body simply won't tolerate one more sip. After having to do a half dozen bowel preps or more you kind of get used to the warning signs your body gives you when it's had enough - lol!