ADS 1501DI 15" Nyloplast Light Duty Round Drop-In Grate. Nyloplast® Light Duty Inline Drains are designed to enter a storm drain line using a tee or elbow and a riser pipe. They represent the latest in storm water piping technology and their innovative combination of performance proven ductile iron grates with a rugged PVC structure makes them unique in the surface drainage industry.