John Boos Action Lever Drain, Fits 3-1/2" Drain Opening, 2" Outlet, with or without Overflow

An overflow is a small hole along the inside wall of a sink that prevents water from spilling out of the sink if the drain is closed or clogged. Water drains through the overflow channel inside the sink until it meets the drain at the bottom of the sink. A drain with overflow holes is needed when a sink has an overflow, in order for the excess water to drain properly. If the sink does not have an overflow, then a drain without overflow holes would be required to prevent any leaks.