Great question — answering as the UphillTech team:
Use a bigger wrench. The "bumps" on the outside of a PVC nut like that are to help a regular pipe wrench grab it. You don't need to limit yourself to a short-handled strap wrench. Also - be sure you've correctly interpreted the orientation of the nut with regards to unscrewing it. The fact that it's upside down has been known to throw folks off and turn the wrong way. Best I can tell from the picture it's probably plumber's putty, and that should not prevent unscrewing it, though it also has no business being there. Edit to add: If you can't get this off even with a big (long-handled) wrench, I would strongly advise not replicating it. The only place I will use glue-in traps is under...
Full answer by Ecnerwal: https://diy.stackexchange.com/a/332026 (CC BY-SA 4.0).
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