How do I connect a 2 inch copper dwv to a 2 inch hubbed copper/brass cleanout?

Sweat it. I hope your torch is big enough. I have an acetylene turbo torch so enough heat is no problem. I've never done larger diameter copper in a heavy fitting with propane, so I can't offer you much help if you don't have the equipment and/or experience sweating copper. I hope I understood your question. The details you provided are pretty sketchy at best.

Hi Jay...

Are you suggesting to connect into an inline cleanout? If so, that really is frowned upon as the cleanout has no DIRECTION built into the fitting and waste materials could get hung up on the threads of the cleanout and cause issues for you down the road, OK?

That being said, if you are still bound and determined to proceed, then at a minimum, you should at least install a new FULL SIZE CLEANOUT just after you connect into the old cleanout.

To connect into the old cleanout you would PRESOLDER a 2" DWV copper MALE ADAPTER onto a piece of copper pipe and then after it cools, wrap some teflon tape and add a little pipe dope to the threads and install to the cleanout. Proceed with regular copper work as needed.

You could also install a 2" PVC male adapter and then a 2" PVC full size cleanout and run 2"PVC to where it is needed and then join to the 2" copper using a PVC to copper SHIELDED TRANSITION MISSION CLAMP (see image below).

Finally, the best job would really be to install a new wye fitting into the copper pipe and proceed, but that is up to you.

Questions? Let me know...

Mark