4", PVC Backwater Valve, Prevents Sewage Or Any Other Fluid From Flowing Back Into A Water System, Elastometric Seal In Quick Action Flapper Ensures A Water Tight Seal, Threaded Access Cap Incorporates A Neoprene Seal For Positive Sealing & Can Be Tightened Or Removed By Hand, Valve Hub Fits DWV Pipe & Can Be Adapted For Sewer & Drain Pipe.