Called the plumber this morning, after more unsuccessful attempts to get at the stopped-up floor drain. They were pleased to tell me they could get around to me...Monday. It was disappointing, but you don't want them with so little work they can't stay in business. They offered to put me on the "standby" list, which I accepted.
Wouldn't you know, Hope Plumbing (they spring eternal)* called in the afternoon and said if I would be home in about a half an hour, a plumber could meet me. Checked with the boss and he okayed it.
$239 and some deft hammer work and a minor drain-snaking later, I have a working floor drain. The drain grate and cleanout were stuck fast; the grate popped out when struck but the brass plug -- much thinner than I expected -- had to be bashed in and replaced by an expansion plug like the one on the main cleanout. A little messy (the plumber cleaned up the very worst of it) but much better.
* One of the very only plumbing companies I know of that keeps chickens. Because who doesn't like fresh eggs?
5 weeks ago