I saw an old TOH in an East Boston house where a bronze drain was soldered onto a shower copper pan. I was wondering how that drain was then connected to the PVC trap? On youtube there's a video done by the "Concord Carpenter" that briefly shows a copper pan going in and PVC coupling has been attached to the brass drain that is then glued onto the PVC trap in the floor. Does that PVC coupling screw onto the brass drain...is it an external or internal thread? or is it done in some other way?