Zero-waste means that 10 percent or less of its waste is trash that ends up in a landfill.
"We had a three-day audit done by a consultant in February, and at that point 11 percent of our waste was going into a landfill. Our goal is to reduce that below 10 percent." (Most of the bar's waste is either composted or recycled.)
I asked Mullins - whose tavern also has plastic cups made from plants, not petroleum - what motivated the bar to go green.
"One, because it's the right thing to do. The other reason is [Drury Street] is cluttered with visual and olfactory pests, and that is Dumpsters," he said. "It's a chronic, horrible situation that businesses can put these Dumpsters here."
Drury is more of an alley than a street, linking Juniper and 13th streets between Chestnut and Sansom.
McGillin's is one of two businesses that front Drury.
"Now, having said that, we have a Dumpster across the street," he said. "It is our front door, but we have all these Dumpsters [Your columnist counted 18 on a recent visit] and only two of those are from businesses on [Drury]."
Mullins said he hopes to persuade nearby businesses to reduce their waste footprint and create a "zero-waste zone."
McGillin's is no stranger to taking a stand against prevailing orthodoxy.
The tavern - like some other local Irish-themed bars - also doesn't serve Guinness, and hasn't for years. The bar boycotts the Irish stout because of what it sees as Guinness' support of "chain" pubs.
"Guinness is everywhere," he said. "Go to any chain restaurant or pub and you can get Guinness. But you can't get O'Hara's, which is the only stout brewed exclusively in Ireland. We also have O'Reilly's, which is made by Sly Fox [a Pottstown craft brewer], a terrific dry Irish stout. The difference is the local product is fresher and unpasteurized. We just like unique products to offer our customers."
On Twitter: @MHinkelman