Winco FB-TS40 Bar Maid Fly-Bye Floor Drain Trap Seal for 4" Drain PipesPatented one way valve allows fluid to flow down without impeding flow rate and lets nothing come back up. Pesticide free, No VOCs Makes drains virtually maintenance free Effectively stops fruit flies and insects from coming up Acts as a vapor barrier to keep bacteria, odors, and gases in the drain for improved indoor air quality No need to add primers and fresh water