For a bit of light relief there was a very funny thread here on SingleTrackWorld of this very procedure in 2009. They use a different laxative today though.
I remember taking " Picolax " when I had my investigations in 2013/2014 . In the first session I had back to back gastroscopy / Colonoscopy. I suppose the thinking was " While he's here we might as well take a look up the other end " I didn't look at the monitor, just tried to relax and meditate, all helped by a wonderful nurse who was sat next to the top of the trolley murmuring reassurances. Fortunately my digestive system was healthy and they even mentioned the thoroughness of my prep work. ( I had started fasting a couple of days before starting on the Picolax regime.