The procedure is performed by a doctor experienced in colonoscopy and lasts approximately 30 to 60 minutes. Medications will be put into your vein to make you feel relaxed and drowsy. You will be asked to lie on your left side on the examining table.During a colonoscopy, the doctor uses a colonoscope, a long, flexible, tubular instrument about 1/2 inch in diameter that transmits an image of the lining of the colon so the doctor can examine it for any abnormalities.The colonoscope is inserted through the rectum and advanced to the other end of the large intestine.ou will receive two enemas before the procedure because the rectum and lower intestine must be empty so that the intestinal walls can be seen. You will need to try to hold the enema solution for at least five minutes before releasing it. Make sure you arrange for a driver to bring you home after the colonoscopy.