My mother told her doctor she could not drink down 64 oz so he gave her something else that was a smaller amount.
I am due for one and going to ask for the same. I weigh 100 lbs and no way can I get that huge amount down and KEEP it down!
Definitely find out in advance what’s suitable for your weight.
On Monday I had my 3rd colonoscopy. The cleansing stuff is much better than it was 10 years ago. I had two 6 OZ bottles of Surprep. You take one bottle and mix it with 16oz of water and drink it all, followed by two more 16oz bottles of water over the next two hours. Then you repeat this a few hours before your procedure. It really wasn't too bad and much better than dying of cancer.