It's the ultimate penetration!!! 😄
It's counter-intuitive how such a long tube, whose length is typically up to some 30" (75 cm), can safely go up the ass, given that the rectum is only a few inches long, before the colon makes several sharp turns. The key is that the colonic tube "swims" around the bends. Therefore, it can only be properly inserted into a colon already full of water. NEVER INSERT IT DRY! If dry, at best it'll fold up like an accordion -- and at worst it'll poke the intestine uncomfortably and dangerously.
Here's how I do it.
First, a preliminary enema (with expulsion) to "clear the way".
Next, I insert just the tip of the colonic tube (no more than a couple of inches) up the ass. Then I turn on the water and wait until at least a quarter of the enema bag is empty. At that point, I insert more of the tube. NEVER FORCE IT! If I encounter ANY resistance, I wait for more of the water to go in, then I try again. If there's still resistance, I pull it out an inch or a few inches, and re-insert it.
A resistance is a probably a sign that the tube is trying to go the wrong way, as it randomly flutters around in the water-filled colon. Pulling it out a bit, and re-inserting, usually fixes the problem. In some cases it takes doing that a few times. But that's part of the fun! It makes a long insertion even longer...
It feels a bit like inserting a key into a lock in the dark. You "wiggle" the key a bit. Likewise, when I insert a colonic tube, I usually go in several inches, then out a bit, then in some more, then out some more...
If you're a beginner, it's best to choose an extremely thin tube -- the kind that's so soft that you could stick it up your eye without hurting yourself! And don't go past 10 inches or so. Wait until you do it a few times and get the hang of it.
The thickness of colonic tubes is measured on a scale called the "French scale". I have no idea why! But "14 Fr" (14 on the French scale) is pretty thin, and therefore soft. "16 Fr" is more substantial, and "18 Fr" even more so. Around "20 Fr" or "22 Fr", the tube starts getting a fair bit stiffer -- and more difficult to insert safely. For beginners, I recommend 14 or 16. The French scale has nothing to do with the length of the tube; it only measures the thickness.
It's common to have little or no sensation of the enema flow when the colonic tube is deep up one's colon. However, the sensation of fullness -- deep inside -- can be absolutely fabulous!
When it's time to remove the tube, do it very slowly. It's a lot smoother to remove it -- and comfortable for the enema receiver -- if the colon is full of water at the time of the removal. In other words, remove the tube and then expel. If you expel before removing the tube, just enjoy re-filling the bowels, and then "reel out" the tube.
(DISCLAIMER: I am not a doctor and cannot give medical advice.