I am also wondering about the "firmly requested"?
We've had the kids have sleepovers in the TT. I can allow them to use the bathroom for #1, but #2 needs the house bathroom. We can rinse out the black tank where we park it at home (basically in the woods), so a little pee doesn't hurt anything.
Friends have had people use their 5th a couple times during family gatherings and it has worked well. Kind of adds to the event!
My Dad needs to be near a bathroom (with no restrictions), and uses a walker, so using our TT would not work for him.
My brother in law once suggested that he wanted to use our TT over one winter years ago... we squashed that in no uncertain terms - he is a HEAVY smoker, even if he didn't smoke in the TT just his person smoke smell would stink it up. Also, he thinks he knows, and can fix, everything - even though most of what he touches ends up being broken.