I'm guessing you're saying this like a mantra some of my old schoolmates used to treat it as, but I hate that phrase. Many places don't have a single soul assigned to clean that area, and the same people who say that phrase are often the first ones to scoff at new taxes to pay for said jobs. My students litter in my classroom without a second thought all the time and then look at me funny when I make them pick it up. I didn't go to college for 6 years to clean up after a bunch of kids, and my janitor's job is to vacuum and empty the trash cans, not put all their discarded paper, gum, and sun flower seeds into the trash can before emptying it.