Usually every seven to ten days. But I recently had severe bronchitis, which made my hiatus hernia and gastric reflux worse. Normally, I take psyllium husk powder every day as a bulking agent to prevent constipation, and my wife suggested I stop it and see if the reflux was any better. It was and I stopped the psyllium husk powder permanently after my next enema.
I have to do daily prostate massage with a fairly large item (a shampoo bottle about 60 mm or 3/8" diameter) or I can't pee within a day or two. I have BPH (benign prostate hypertrophy). To keep things clean for this, I shove the bottle up into the descending colon as far as it will go, then come back down at attack the prostate. Normally, after an enema, it used to take about five days for any crap to appear in the lower colon, but this time I noticed nothing at all for eight days. When it appeared, I pushed it back up out of the way as usual and carried on. Obviously, there was much less crap there than formerly. To cut a long story short, I went 16 days without a BM before deciding to do an enema series. I like a full bowel for a satisfying expulsion, and this was a good one.
The next cycle I worked out that the shampoo bottle 'pusher' was compacting my bowel contents and I liked it! I had, of course, gone back to being pretty constipated. Again, I only started to feel any crap low down the descending colon after seven days. But this time I was still quite comfortable after sixteen days, and then a series of circumstances prevented me from doing my enema series for another week. There was no longer any urge to empty my bowel at all - indeed, with a finger I couldn't reach the mass inside me. In bed, however, I could feel the leading edge of the it inside of me through my abdominal wall! It finally formed a visible bulge on my abdomen, which moved depending on which side I was sleeping on!
I finally took the enemas on day 26, and the expulsion was spectacular! It blocked the toilet immediately, and the water level rose and rose as wave after wave of stuff and water poured out of me.
That was fun, and I'll probably do it again!
Johnny