I know the ISO ratings are not overly useful for real world capacity, but they can be useful for comparison.
Is there a list anyone knows of that has various adult diapers, pullups, etc?
Not that common in my experience. It's a different with really young babies who wake up in the middle of the night to feed - their GI tracts are pretty much always processing, because they eat at intervals around the clock. But by the time my kids were sleeping through the night, "the morning report", as my wife & I called it, usually came sometime after breakfast, once things started chugging along in their tummies. I think it's similar to what adults experience - getting up to pee is somewhat common, and more so as you get older - your body produces a hormone that lowers renal output when you're sleeping, but doesn't completely eliminate it, and that can conjoin with the reality that, for men, ever-growing prostates create a restriction that tends to inhibit complete bladder draining, so that a "reserve capacity" is always in there, effectively reducing the timeline from "empty" to "gotta go" down to a few hours, hence nocturia becomes a thing.
But unless you ate something that disagreed with you, or you're taking medication, getting up in the middle of the night to poop is a less common phenomenon, because the works down there throttle down while you're sleeping. It's the same with kids once they're not eating at 2 AM and again at 6 AM or whatever the interval is.
This is a wonderful story that I am enjoying quite a lot!
There is one feature that makes following the progress somewhat difficult, however. His/her, she/he are used interchangeably throughout the story and without respect to the character's gender. I offer this simply as constructive criticism, and hope you continue this delightful tome.