I am pretty new to this stuff but I have unclogged a couple P drains in my time. I am attempting to replace my bathroom sink but I couldn't find a pipe fitting at Home Depot that looks like the following :


Everything I saw at home depot was just straight through. I think this is just overflow in case the adjacent guest bathroom on the other side of the wall gets clogged or something.

Anyway, any opinions or guidance would help? Do I need to go to a plumbing supply house for this. Home Depot is really the only "big" place within 20 miles of me.