TUF-Tite 20" Heavy Duty Flat Lid - Septic Tank Lid - Septic Tank Cover Tuf-Tite Flat lid for septic tank risers Fits on 20-RIS Round Riser, 20x12-RIS Round Riser and 20-RISP Safety Pan Fits most commercially available:Risers , IPEX-PVC Ribbed Pipe , Corrugated Pipe