My shower/tub upstairs drains into the downstairs toilet causing it to overflow, why?
We have lived in our town home for almost 2 years and never had a problem with plumbing other then the customary plugged toilet. The last week whenever some takes a shower or tub upstairs it drains down into the downstairs toilet and sink. We have snaked it and also had a plumber out here 2 times and it is still doing it. When we flush the toilet both upstairs and downstairs they flush fine but when we shower it drains into the toilet downstairs and overflows it all over the floor. Any answers would be helpful. Someone told me there is a vent on the roof over the bathroom and that it may be clogged... I.E. bird nested there or just covered with leaves or such... we are going to check that in the morning... need help fast... we have spent almost 5 hundred dollars in the last 2 weeks on plumbers and laundromats.