Water backs up into downstairs bathroom sink.
Hello
HELP! My situation is... water backs up into downstairs bathroom sink apparently after the upstairs shower has been used which is directly above the downstairs bathroom. Our house is around 40 years old. We have had people there before and opened up the wall on either side of the downstairs bathroom and replaced the "Y" joining of the pipes, as well as the piping under the sink downstairs about 6 months ago or so.
The problem has just come back. Any clues what IS REALLY causing this again?. HELP!!
Thank you in advance!