Thanks so much for the replies, and pics!
I am now pondering if I can install a standard RV toilet (
https://www.etrailer.com/RV-Toilets/...c/DOM87FR.html) and squeeze in a tiny black tank (
https://www.recpro.com/13-gallon-rv-...tics-epi-199h/) in place of the current under-plumbing. And of course, snake in the gray pipe so all the flushing works.
My TM has a 4-5" lift, so... will measure soon and see if I can find a small enough tank.
Am I missing something...? Can't imagine why no one else would've done this already.
Thanks again,