@MrsPete
The low volume prep is called Suprep
It's two 6oz bottles of prep liquid that you drink straight, followed by 2 more 16oz cups of water afterwards, but you get an hour to get that water down, so it's pretty easy.
This is what I was given when I had a diagnostic colonoscopy 5 years ago.
The liquid does NOT taste good. It's supposed to be "lemon lime" flavor, but it has quite a sickening, salty sweet flavor. I chilled mine and chugged it, and ended each bottle with a strong gag that almost brought it back up, but I followed the advice of the nurse and chased it with a few sips of ginger ale IMMEDIATELY to get the taste out of my mouth. The fizz from the soda sort of confuses your nervous system and stops the gag reflex. Neat trick.
Anyway, I found this prep made me "go" quite quickly and fully, without any discomfort, nor was I in the bathroom for hours. Literally 2 quick trips and that was it. One more trip the next morning after the second bottle, and that was all just clear liqiud at that point. It was not what I expected based on what I'd heard.
I'd request this prep again.