Josam 21503-z large sump roof drain w/poly dome and 3″ no-hub outlet cast iron roof drain, large polypropylene locking dome, wejloc non-puncturing clamp ring with integral gravel stop, large sump with wide roof flange and bottom outlet. used on roofs of any size, for any type of construction. large slotted dome provides 124 sq. Inches of free area for quick drainage of rainwater and protects the drain sump and connected piping from debris.