we are in the process of modifying some rooms and we have an existing 3" pipe with a 1 1/5" drain pipe as shown here:
We're trying to add a sink on the side currently not serviced by the drain pipe and as far as I can tell we have a few options:
The most difficult option, but probably best, would be to cut it all out and at the bottom, use a wye with a 2" coming off it do service two sinks but that would be really difficult at this stage of the project.
Outlined in red below: 1 1/2" pipe for all connections, add a double sanitary tee at the top of the pipe, optional mechanical valve.
Outlined in blue below: 1 1/2" pipe for all connections, replace the top tee with a double sanitary tee.
We're in Michigan, is any of this is good or up to code.