I'd suggest trying toilet bowl cleaner if it's really shellac or similar. Let it soak for a few minutes and wipe with a heavy cloth and/or rinse with a hose. Wear non-absorbent gloves. Wash off any cleaner you get on your skin. I've used this to turn #2 to "Bright and Shiny", but really wasn't worth the time and effort. In this case, it would be.
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