bosco123,
Yes, you have to drink the whole thing. I specifically asked my doctor and he said - got to drink the whole thing.
I had alot of trouble just drinking it down, it made me feel like I was drowning in liquid, it was an awful feeling.
And then the "cleaning out" oh, that was fun. I felt like my colon and rectum were on fire the whole time. Not something I am looking forward to repeating.
Luckily, my GI told me I'm due dor my next one 3 years after the first one.
The "out of it" feeling lasted about 45 minutes, until after the effects of the anesthesia wore off.
But I should warn you about the GAS, painful gas, that you'll probably get from the colonoscopy. It comes from the air they pump or goes into you from their instrumentation, seems it's quite significant.
You may feel a little weak the day after...hopefully not.
Good luck with the colonoscopy, let us know how it goes.