On Monday, May 17, 2021 at 1:31:30 PM UTC-4, Na'ilah wrote:
Thanks, TimR. Pretty sure drywall mud, etc. would not cling to a vertical pipe...

Are you saying lime scale would not be that thick or easy to scrape? What would you expect with lime scale? (This stuff was the texture of frosting mixed with sawdust.)

Also, maybe it's possible wax from the ring may have been in the mix, but it didn't look waxy/greasy/shiny at all.
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Have you ever tried to scrub lime scale out of the inside of a teapot? It's almost as hard as the metal. You might dissolve it with something acidic but abrasive pads don't even dent it.

Yes drywall mud will definitely stick to the side of the pipe but I would have thought that would be more solid than you describe. So I don't know. It sounds like something got poured down that shouldn't have been, but I'm not sure what.