Introducing the ultimate solution for connecting 4 in. SDR 35 and SCH 40 PVC to 3½ in Corrugated – our HDPE coupler. Built to last, our coupler is made from the strongest material on the planet, HDPE, which boasts a lifespan of up to 500 years. Not only is HDPE durable, but it’s flexible enough to withstand underground buried downspouts, which is crucial when the ground settles and shifts over time.