@mikec415 @georgetakei checks notes.
I had a CT scan recently to complement a colonoscopy that had already found a colorectal tumour.

That only required me to:

"Drink 750 ml of clear fluid (water or juice) slowly at home during the hour prior to your scan. It is important you do not drink the fluid all at once. Drinking the clear fluid improves our ability to see the organs within your abdomen and pelvis clearly on the scan."

My CT scan was 'with contrast" which meant that they injected a dye into my though a tube inserted in to my arm during the scan. Gives you a warm feeling like you are peeing. Your kidneys have to get rid of it after.wards. I could feel they were working quite hard.

Though I suspect there may be variations in what prep they ask for. Mine was done in the UK.