BrassCraft® 5/8 in OD Inlet x 7/8 in OD Outlet Dishwasher Air Gap with polished chrome . Used to ensure that waste water is not siphoned back into the fresh water supplied to the appliance. An air gap also provides an alternate water drainage route in the event that the drain hose is clogged, water may flow directly into the sink. Required by many local plumbing codes.