Prostate exam is a rubber glove and a finger.
For a colonoscopy, you spend a couple days prior taking stuff to make you crap, and only taking in fluids. You are very clean after the prep. The prep is the worst part. The procedure, you are drugged out, and then wake up. They insert a tube with a camera and go all the way to the end of your colon.
Important - they can also remove pre-cancerous polyps with the scope. I know for a fact I saved at least one man's life by urging him to have a 'scope, they removed 3 pre-cancerous polyps.
For someone obsessed with enemas, you sure are phobic about this.