No offense, but one the the worst plumbing jobs I ever saw was done by a guy that worked for a supply house. After you replace the section in question with the one recommended by the supply house, where exactly will the drain to the shower be?
And you still need to confirm that the drain you want to tie into is connected to the sanitary sewer, figure out why the trap fills by itself, figure out the venting, and learn how to properly install the various fittings and pipes required to complete the job.
Have you pulled a permit for this job?
You very well may impress the wife yet. Or get to spend some quality time on the sofa after you flood the basement.