Quantity of (6) : AmeriMax # 4400 InvisiFlow 18" Flex-Grate Black PVC Downspout Filters . InvisaFlow Flex-Grate Filters Out Leaves and Other Debris , Preventing Labor Intensive Downspout Jams. The grate diverts gutter debris , allowing water to flow through and drain correctly. The FlexGrate keeps landscape drain pipes and rain barrels free of leaves and debris.