How to convert 1 1/2 inch drain pipe to 2 inches coming from my basement floor?
If in your picture, the clean-out has a 1.5" to 3" adapter on top, which is glued to the clean-out and the 1.5" above, you will need to replace the clean out. It looks to be 4" bottom, 3" top. Ideally cut about 1" above the bottom of the clean-out, and cut vertical grooves into the remaining clean out and remove the last 1" with pliers. Hopefully if you do that you won't loose any 4" pipe, as you don't have much exposed. May need to sand/clean up the pipe for the new fitting. Then put in a new 3" to 4" clean out. Then you can put a 2" to 3" adapter in, and replace and necessary Ts and piping above to 2".