John K Jordan
I also used the 6" S&D pipe from a plumbing supplier with five 6" drops, some split into several 4" lines. I found the cheapest elbow and wye fittings at the local Ace hardware. I use a 5hp ClearVue cyclone and the dust collection is amazing.
But you didn't mention what dust collector you have. A larger pipe is not necessarily better if the dust collector doesn't have enough power to keep enough air moving.