Thank you Thank you Thank you to BSR & ToyMaster for their invaluable non-HA but WAF-critical assistance last night on my plumbing. I described my very non-HA issue, they immediately said "sounds like a blockage further down".
Yep, that's what it was. I took my P.O.S. $30 snake, rammed through one block, hooked pipes back up, didn't work, did it again, found another blockage 18" further down, and now it works!
I was *this* close to having wife tell me to drop all the HA stuff this weekend and work on that.
Back to drilling holes in the walls & ceiling.