NDS Catch Basin Extension 24 in. x 8 in. Black. Need to capture surface water with a catch basin that sits deep in the ground? Give the basin a boost with the 8 in. Riser. Fits on top of the 24 in. Square Catch Basin Drain and adds an extension of up to 8 in. of height to reach the surface. Riser can be cut to size for custom height. The 8 in. Riser for 24 in. Square Catch Basin Drain eliminates the hassle of regrading elevations or awkward piping. Made of durable high-density polyethylene (HDPE) treated with UV inhibitors.