Is it OK to expose drain pipes on the exterior of your house?
I spoken with the San Francisco Building Code inspector and they said ABS exposed pipes are allowed as long as it is coated with UV protected paint since it’s located outdoors.  Also ABS used for DWV applications are only allowed for buildings up to 2-stories private and commercial. For mixed material couplers, I would need to find a coupler made specifically for steel to plastic.  Thanks @jim for telling me just to call the inspector.