Polyethylene riser lids from Hedstrom Plastics fit standard 18- and 24-inch double-wall corrugated pipe. Gaskets and safety hardware are included, and a safety net is available. Covers can be filled with sand on site for added weight. Foam-filled lids are available upon request. Covers can be customized with the service provider company name and are available with a tank adapter. 888/434-5891; www.hedstromplastics.com.