Prove, not prove, that’s not really the issue. As unpleasant as the bowel cleanse is, the cleaner the better as far as finding and identifying any anomalies goes. Your friend’s bf has some serious issues that preclude having the full cleanse, but the result may be more problematic than if he was able to do the whole thing. As much as I detest the full-on event, I’d rather have my bowel the cleanest possible before any test. I hope your friend’s bf is better soon.