Constipated preschoolers (yawn)

I read on one of the forums I've been banned from - for the crime of telling inconvenient truths about habitual constipation and how best to manage it - that a three-year-old kid on the equivalent of miralax is still withholding with all his might and only ever leaking little dooey-smudges.
What I should be able to say on that forum is that, if that happens, it's time to finally introduce the thorough purge which you should be using anyway - an enema. Apart from giving you the chance to take control and do that kid properly - hold him down, force in the nozzle (it'll make him scream-cry) and inject, I suggest, a 40ml bulb of mixed water/glycerin - you can then sit him on either the potty or adapted toilet and make him stay there until all that filth and stink has come blasting out of him. And in this way, sternly teach him what are the immediate perils of excrement-withholding - "do, or you'll get done"