[Tidybuoy]

I'm putting on a new roof and I want to merge three 1 1/2 steel pipes with a single 2" pipe coming out of the roof. These are all plumbing vents and based on my research this is OK to do via my local codes.

The one 2" Pipe that will remain is a non-removable steel pipe (i.e., it goes down the wall into the house plumbing and there are no joints in the attic).

My plan was to cut the 2" pipe in the attic and install one black PVC 4-way connector and then re-install a portion of the steel pipe to exit the roof.

Can I mate smooth PVC connectors to a cut pipe or must I connect using threaded pipe. I can use threaded connections to all of the 1.5" pipes because they all have joints in the attic but the 2" pipe will need to be cut and then mated to the PVC. I don't have access to a 2" threader.

I figured I could just put it all together like tinker-toys and not worry as these are just vent pipes and won't have any water pressure in them but I thought I would check to see if anyone knows the correct methods for doing this. All of my pipes will be downward flowing to prevent any rain water from sitting in them. I'm asuming the PVC cement won't work with the steel but I will check at the hardware store.

Thanks.....Vern