The plumbing story part two:
Handy cleaned out the trap in the upstairs bathtub (through the hole in the wall) but blub blub blub. No noticeable improvement.
We called a plumber, who wasn't too interested. I think they only like to deal with the emergencies. Days later a guy showed up, laughed at Handy's redo, and said we should tear out a wall. We were supposed to get another call back this weekend but no nothing happened.
Meanwhile, Handy bought a better (drill-powered) snake and solved the problem himself. Ernest ran water in the tub upstairs and said he'd never seen it drain so fast.
Really, learning to do your own plumbing is where it's at.