It's a long and very weird story with diapers, bondage, and inanimate TF.
You can wiggle your way in and tape it up nice and snug, but your legs won't close once it's done.
You waddle around with some effort, but you're not going anywhere fast.
It does get easier the second time; easier than you even expected, actu- whoa, okay. Didn't realize you had that much in you.
Before you can process what's going on, you bear down reflexively and fill the back. Not the slightest hesitation once your bowels give even the tiniest hint of movement.
You end up on all fours, panting and grunting in desperation - it's as if it's coming out of you in one constant flow.
(Defcon 3 weirdness coming up, fair warning)
The plastic spreads, slowly covering you up in snug, crinkly padding along with the ever-growing load inside.
Your surprise is met by another powerful urge to mess and flood the padding, which distracts you again so that it can continue to spread.
Strangest of all is that you don't feel your clothes any more. Just the padding and its contents.
The tight fit of the crinkly, wet padding forces the soft mess to spread all around you, filling every bit of it.
Your meager struggles get you nowhere; your hopelessly mittened paws now have no purchase on the tapes that seal it around you.
(Defcon 1 weirdness coming up. I'm serious.)
As it presses down on you, it forces the soft, loaded, used padding against you - to the point where you start to lose sense of where you end and the mess begins.