Between pipes. Mine is slightly different, kind of steel wool, but this one would do. Maybe I will also use exhaust cement from Autozone.
https://www.walmart.com/ip/Scotch-Brite-Stainless-Steel-Scrubbing-Pads-3-Pack/13281617
https://www.walmart.com/ip/Scotch-Brite-Stainless-Steel-Scrubbing-Pads-3-Pack/13281617