Colonoscopy Procedure

I want to get a colonoscopy every year, but since taking a lot of medicine and water the day before and emptying my bowels is painful, I have been substituting it with a stool sample every year lately. Then, while I was at the park, a woman told me that on the day of her colonoscopy, she administers the medication at the same time as her gastroscopy to make the process simpler. So I checked with a hospital and called them; they confirmed that administering the bowel-emptying medication during the gastroscopy allows for a complete bowel emptying in a short amount of time. However, seeing that major hospitals do not adopt this method, it seemed there might be some issue.