So I took the plumber into the other bath, water closet, reading room. The tub in there has never drained properly. He worked on it. No gray hair. This time he pulled out a piece of flexible plastic pipe from the drain. It was left by the initial tub installer.
Now they both drain like real troopers. $247. Yep. $247. I suppose there would have been a cheaper way. Sledge hammer and drill bits. I liked the plumber. He didn't even make fun of me. Actually he was real serious the whole time. I woulda thought plumbers would be a bit more jolly.