Barry Irby
I was thinking about this idea. I am guessing the run is fairly long. Your two inch incoming line is probably very rusted on the inside and may be partially closed off. (Iron expands about five to one when it turns into rust) It might be worth investigating, but I seriously doubt it will be simple to slide a new pipe inside the old one. If somebody had a roto router type device to clean the inside and smooth out the rust-cicles on the interior it might be possible. My usual experience with this is they charge so much more for the high tech approach its just as expensive as the old fashioned brute force approach. Still might check it out.