Thank you for the replies. By the way, the floor is tile over a concrete slab. I sat a level on the floor both vertical and horizontal, the bubble was slightly off barely touching one of the lines in the sight glass. Perhaps the house has settled a bit over the years, I don't know.

I like the grinder idea and stuffing rags down the pipe to catch debris. Since I have never done this type of repair before I am thinking of trying to source a piece of scrap cast iron drain pipe to practice on FIRST.

Practice makes perfect!