I have been using colon tubes for enemas for quite a few years. SwSusie's advice is spot on. Pay attention to it. I have 3 colon tubes, all 30". Two are 36 Fr and one is 42 Fr. Two are rubber and one silicone which is 36 Fr. I've had the most consistent success with this one. Here's what I've learned over the years that works for me:
1. Take at least one 2-3 quart regular enema first and make sure you have fully expelled it.
2. Use LOTS of lube. I will lube by anus with vaseline and get some as far inside as I can. I have a lube shooter which I'll fill with KY and insert into my rectum and discharge it as I pull it out so there's plenty of lube throughout including on my anal opening so the colon tube picks up the lube ss it passes through my anus.
3. BE PATIENT. This is an absolute. You force a colon tube or you quite probably will end with the the serious and quite possibly life threatening complications Susie describes.
4. I insert the colon tube maybe 6-8 inches into my rectum until I feel resistance. I'll start the water at that point and wait until my rectum fills before attempting to gently insert it further. If it wont go, dont force it. Turn it or make it go in and just a bit. As the water fills your sigmoid, it should be possible to insert the tube further.
5. I've found that getting the tube through your sigmoid and into the descending colon is difficult but if you are PATIENT and go slowly, most of the time you can do it. You'll know you've gotten around the first bend because all of s sudden there is no resistance and you can fairly quickly insert a 30" tube almost the whole length.
6. A 30" colon tube, I think, will go to the bend that separates the descending and transverse sections of the colon. Once i feel resistance again, I stop. I have never attempted to go beyond that point and never will.
7. The point about having a colonoscopy done with sedation is important. I have done that because I really did want to see what my colon looked like snd because I wanted to feel what the procedure was like as well. I accomplished both. I will say that doing this without sedation is not for the feint if heart. It was uncomfortable. I have a very high threshold of pain so I got by that. If you don't, I'd think twice about doing it.
8. I love colon tube enemas. I love the feeling of the tube sliding through my anus both while being inserted and removed. I've described it as almost like being fucked by a long, thin cock. But, unless you're doing it with one of those big colon snake enema tubes, there's no way even a 42 Fr colon tube in a well lubed anus and rectum is going to provide much in the way of prostate stimulation.
Thus my much more than two cents on the topic.