Have a very slow draining main line, which has now backed up sewage into the downstairs shower and basement drain. It will drain, but takes several hours. Previous owner built the basement bathroom wall over the clean out port, I would have to take out most of a wall and it looks like probably chip out some concrete as well. The plumber said the other option would be to take off a fitting to the main 3" pipe and run a snake from there towards the street. He did not know what might be slowing the flow whether roots or something else. He indicated it would cost about $1200 to do this, which I can't do right now. Can I install a clean out port myself in that main 3" pipe (the one that goes down) and could they then snake from there to the street? That would save me about $400 according to my quote. If I did that is there a snake I can rent, and how hard is it to use and how risky to my plumbing?


Is it worth trying the Main Line cleaner products or try a root killer since I don't know what is causing the slow flow.

Either you have a plumber that's too lazy to climb up and snake from a roof vent or he just lacks the experience to do the job. It sounds like you have two places that needs to be snaked.
1. Snake and clear the shower drain. **AND**
2. You have a blockage downstream from the basement shower and floor drain. I would snake that from the floor drain.
Locate the house cleanout and open it up. If you see standing water then snake to the street. No need to tear anything up. And get a plumber in there that knows what he's doing. Good luck, Tom