I have a three story house. Bathroom on top floor drains on the interior wall going to the basement. Any flushing or draining is heard in the living room and the guest bedroom. House built with plastic pipes. How can I reduce the noise or best of all do away with it all. Some suggestions have been, replace plastic with cast iron (means tearing out the wall), pump insulation (sound) from the top of wall, open wall by the pipes and insulate with that foam stuff. You suggestions please and a basic est. of cost.