John Deere Landscape Supply in San Carlos has a wide selection of 6 inch and 8 inch PVC pipe and fittings. Some big box stores have 6 inch black ABS pipe, which I used in my shop in San Mateo. I liked the ABS, as the fittings are designed for sewer systems, so extra long sweeps are available. Some ABS fittings will take direct connection to DC fittings that most woodworking stores sell. A nice bonus.