The bathroom sink drain is so slow I cannot use the sink anymore. I have removed the trap below, and checked that, it is clear. I put a snake into the drain pipe that enters the wall, and it has a black sooty coating, but the snake does seem to go about 6 ft. before stopping. Must I replace all the pipe from the wall to the vent stack, or would a roto-rooter type tool be able to open up this pipe? The wall will have to be torn out if I have to get to the pipes inside the wall. Any other options? Thank you.