I'm not an expert or anything like that, but I do know that when someone is having medical imaging tests for polyps in the colon, they must have a barium enema, where a substance, called barium, is put into the colon so that an imaging machine, maybe an x-ray machine or a CAT scan machine (which takes many x-rays of the structure of the colon), can pick up any irregularities, like polyps. Polyps may cause you to bleed out the rectum when you sit on the toilet. It is important to have this type of enema so that the x-rays will show the structure of the colon.
Your father may or may not also have a colonoscopy. This is where a tube, with a camera and light on the end, is inserted up into the colon so that the doctor can actually see, with his own eyes, what the surface of the colon looks like. He can also remove any polyps that he finds right then with a special tool that is on the end of the tube.
My mother-in-law had this procedure done just recently and had a polyp removed. She had been passing alot of blood and having alot of cramping. She was diagnosed with ulcerative colitis. This is an inflammation of the colon. The polyp did not cause the colitis. They are two unrelated conditions.
I hope this information helps to answer some of your questions.