The air gap body separates the hose running dirty water from the hose running to the drain. 5/8 Inch x 7/8 Inch Dishwasher Air Gap Body with Flanged / Skirted Chrome Cap Since these two paths never intersect, there is no risk of wastewater creeping back into your clean appliance. It is a simple way to make certain wastewater and debris never re-enter your clean water supply. The dishwasher air gap is mounted above the sink and prevents contaminated water from re-entering the dishwasher from the drain via backflow.