I am building my ductwork out of 6" PVC drain pipe. The only problem I have had is in the locations that I have used flex lines to complete a drop. How have others joined the flex line to the PVC? It fits inside of a PVC fitting, but will not go on the outside of a pipe so that it can be clamped. My best solution so far (that I am not thrilled with), has been to buy 6" metal duct fittings (maybe called starters or stubs IIRC). The ones I used come flat and you snap the ends together into a round fitting. I have inserted the finger side into my PVC pipe and run a few screws through some of the fingers. The flex line fits the other side well enough with a band clamp. My biggest complaint is the deformity and possible potential for turbulence where the fingers enter the pipe, as well as the fact that the flange that divides the finger side from the solid side is slotted and allows leakage. I suppose the leakage can be alleviated with duct tape, but I was wondering what others had done.
SteveP.