Topp B2406EXT 24" x 6" Recessed Rolled Top ExtensionTOPP Recessed Rolled Top Extensions The Recess Roll Top Polyethylene Extension was specifically designed to conveniently and easily increase basin depth quickly. This product provides a smooth and flush appearance, once the installation of the cover is completed and can be installed on a number of our polyethylene basins. The wide upper flange also helps prevent dirt, gravel and concrete from entering the basin during installation.