How exactly do you tie it in with the pcv, and where do you get your materials?
I use a Fernco - Proflex model ( 3001- 43 or 3001- 44 )
, depending on downspout size ( I use either 3 or 4" copper pipe ). I get them at a local plumbing supply just call arround, you may have to order them but a larger PS should have them in stock. I pay around $ 8.00 ea. for them. make sure you get the 3001 series ( plastic to Copper ). I use a 4" street 90, then tie that into the copper with the Fernco.
They make a special lube to help slide the Fernco over the pipe, I highly recomend using it.
Best of luck,