I have noticed that beyond a certain distance, maybe an inch and a half to two, into my little anal opening, there doesn't seem to be any more tactile sensation on the walls of my colon. For my enemas, I normally use a 'standard' adult rectal nozzle, which reaches about that when fully inserted. My major 'feeling sensations' are the sliding in and sliding out of the nozzle, and of the temperature of the nozzle (which reflects the temp of the solution) and any flowing of solution that touches the wall where there is still tactile sensation. The expansion of my colon because of the volume of the enema liquid squeezes the interior of my abdomen, and causes me to feel full, and I am sure triggers other sensations which I don't directly feel, but result in my feeling cramps, and the urge to expel. However, if I use the 'douche' nozzle normally supplied as part of a 'combination set', with its little sideways jets, the sensation of feeling the liquid flowing in, is enhanced (for me, anyway) because the flow can be directly onto something that can actually feel it. Coming out the sides, the solution directly impinges (hits) something that can 'feel the touch'. Here is the relevance: For me, if I slide such a nozzle too far in, it goes beyond where the jets can be directly felt, and it just becomes a larger bore delivery device (about four times a normal standard adult rectal); to gain what I see as an advantage of using a douche nozzle, it should be only slid in a certain amount so that the feeling of the solution 'rubbing' me as it flows against those sensitive tissues is reached. This mechanism is like that of running water over your hands; sure you can feel the temperature, but you also feel the pressure of the running water as it hits your skin. Now, if this is not an objective of yours, slide it in as far as you like; but beware, the lack of tactile sensation beyond a certain point could mean you can't feel an impending accidental puncture. Colon tubes, I understand, are properly finished (smooth ended) and soft to prevent such problems. But the 'standard' rectal nozzles, and other hard plastic products can potentially be hazardous.
As for how enema insertions are depicted in commercial enema videos, where quite often a douche nozzle is used, and it is only partially inserted, well, that is stagecraft. I enjoy viewing it, vicariously wishing I were there, etc. Who knows whether the actual sensation (of the actress receiving) is even considered; somehow, I suspect that the amount of fluid that actually flows is probably not that great (if any at all); I mean, can you imagine having to do a half a dozen 'retakes'? You do the math. π π π
C.