@CsawDL
In your OP about diaper punishment ideas, you mentioned a hollow butt plug. This is an interesting topic because, like having an indwelling Foley catheter, once the device is in a person, they are deprived of all control of that bodily function, a very primal instinct. Almost the first thing a baby really has any control over is their poo and pee, and a hollow butt plug completely strips the wearer of that capability.
Once a Foley is in someone, they will pee. There is absolutely nothing they can do to stop it. They will pee until their bladder is empty, then dribble pee thereafter. No amount of clenching or any attempt to stop the flow makes the slightest bit of difference. Furthermore, with the Foley balloon inflated, it is all but impossible to pee out the catheter. Face fact... you will have no control at all. End of story.
Similar things can be said about a hollow butt plug, either metal or plastic. While they feel quite different... the metal ones feel "heavy" and unyielding, and the soft plastic ones feel somewhat "squishy", either will hold the passage open so there is no chance of any control over your poo. If there is soft poo in your rectum, it's going to come out. It cannot be controlled. If shopping for a butt plug, you might want one with a removable core, to ease insertion.
For best effect with a hollow butt plug in, you want the poo to be very soft, but not liquid. So that pretty much rules out an enema, certainly a large one, but probably a small one too. It'll dribble out and hence won't make you poo, at least not big time.
If you are constipated before the plug goes in, anything that makes you poo is likely to also expel the hollow plug. The plugs don't retain as well as a Foley catheter, which gets inflated after insertion.
So, for best punishment, if you are wearing a hollow but plug is a strong laxative that will make you poo but not result in a very liquid mess. This is not difficult to do, but does take some preparation. That starts two days before your planned diaper session and goes like this.
Two days before, you eat a high fiber cereal for breakfast and/or take a full dose of a fiber supplement, plus an Imodium tablet. Lunch and dinner are high fiber again. The same routine is followed the second day. By now, your bowel should be full of poo.
Assuming the next morning is playtime, after dinner drink two, or even three, doses of Miralax. You should get this down well before bedtime. This will make all that poo nice and soft. At bedtime, take two Maximum Strength Senna pills (50 mg senna total), insert the hollow plug, and put on your diaper and plastic protective panties. Senna is a stimulant laxative, but doesn't soften like Dulcolax, so you won't get liquid poo.. Sometime, in the next approximately 12 hours, you will get strong cramps and uncontrollably fill your diaper with a lot of soft poo.
You will completely lose control and will not be able to stop going.