The Westbrass air gap shields dishwasher dirty water from backflowing into your dishwasher and onto your clean dishes. The air gap also shields the dirty water from overflowing into your main water lines, as required by code in many states. Cap leaves lip of air gap body exposed when installed. Do not use plumber's putty for installation use silicone to seal to sink. Available in a variety of stylish finishes, this item is sure to complement your existing fixtures. Westbrass Fine Decorative Plumbing since 1935.