"Another note ... I've asked several questions as I've continued this story, and they've gone un-replied to. That indicates to me that folks have quit reading this ... sorry if it became boring but I wanted to post my explorations story, start to finish, in one place."
I think it is common, especially after one gets a new trailer and are all engrossed with figuring it out, to assume that everybody shares one's enthusiasm and urgency. I have this issue with my wife- I get all interested and involved with some task( a new truck, boat, idea....) and though she shares my interest- not quite as much.
At any rate- keep in mind it is the fourth of July holliday and summer and lots of folks are out camping and not actively online. It also isn't unusual for folks to be tuning in only every couple of days or, even, weeks. So, I know when I have a burning question even though I am hoping for an immediate response----people tend to get to me when they get to me... sometimes I'll get a response a couple of weeks after i post. Often, I think, people simply don't have an answer.
or,they don't have that much interest at the moment.....which is ok.
At any rate- as to your last plumbing question- I don't think you are likely to see any actual "pipes" etc under the trailer that you can trace to the holding tanks---at least I do not recall seeing any under mine. Most of those runs are done internally-so I think what you are seeing is what we all see unless you definitely have a pipe you are tracing from the shower, say, to the black tank. All in all, that trailer seems to be working fine.
Hang in there-
rick