I've consistently turned down my doctor's yearly offer of a routine colonoscopy because of instrument sterilization concerns (thanks Dr. Mercola for that alert), risk of perforation, potential disruption of gut microbiome with the required prepping plus some personal concerns about possible medication side effects. It would be a different story if I had symptoms needing diagnosis, but as just a routine annual thing the risk/benefit ratio isn't there for me right now. If I did develop a need I'd definitely want to know ahead of time what they used to clean that scope.