We have a sink that drains slow. I fix it and it is back to draining slow again within a few months. The solution is to replace the drain pipe in the wall. The current drain pipe, galvanized pipe that was very rusty was a tee in the wall with the drain pipe running down and the vent pipe running up.
Step one was to remove the siding from the house and remove the tee and the pipe above and below the tee. Inspection of the offending tee can be seen below.
Once the siding was removed another problem was found. The vent pipe had a section of black iron pipe that had rusted. To remove that section, which rested on some blocking to support the pipe, I had to support the pipe in the attic. As for the rusted out 4″ section of pipe, it had to be replaced.
Once in the attic, a couple of 2×6’s were used to support the pipe as it ran parallel to the roof. Additional support was put under the pipe as it entered the wall headed down to the place the pipe was cut. With the support coming from above, I could take the pipe fitting off the threads so that I could put a new ABS fitting on. To take the fitting off, I needed to use a ratcheting strap from the pipe to a tree to pull it away from the house enough to get a pipe wrench on the fitting.
After a trip to Home Depot to pick up the parts I put the section back together with a new sanitary tee going into the house. Of course that cannot be seen because it is being the siding and trim that I did not remove.
From there wit was off to connecting the sink back up in the house. Of course I took time to install the new faucet that I purchase some time ago. Fancy that, no more dripping and a sink that can drain. Just another day with This Old House.