if it's yellow, let it mellow; if it's brown, flush it down

— [Robyn] Griggs [Lawrence] tells them [the audience] they can make a difference without spending thousands of dollars: Line-dry clothes, vacuum refrigerator coils, and reuse greywater—water that’s been used once but is clean enough to use again—to irrigate the lawn or fill up the toilet tank. She recites her own family’s mantra regarding toilet-flushing: “If it’s yellow, let it mellow; if it’s brown, flush it down.”