I have been having this problem on and off for the last 6 months. I will get it fixed (myself through chemicals, hot water, and/or plunger) or twice to a plummer. I feel like the plummer is missing part of the problem since it keeps coming back and at over a hundred dollars a visit, it's time I get some more advice.
We have a two-story townhouse, built in 1980. The first time we had a problem, we had two people showering upstairs and a bunch of sewage came up in the toilet and bathtub downstairs. We called a plummer and he snaked a drain outside, I think going to our main drain into the street.
A month later, similar problem running water upstairs (and dishwasher, but don't know if that added to the problem) and the same gross water backed up into bathtub and toilet downstairs.
Again later, I ran a bath downstairs and it would not drain. I immediately had problems flushing same downstairs toilet. When I would plunge the toilet, I could get it to drain but backing up in bathtub starts back up.
We have been lucky to keep the problem for getting out of control, but once it completely flooded our downstairs (I have tile and wood laminate flooring, which caused a little puffiness and creaking around in the floor now). But when this happens, we have to be careful with showers, washing dishes, flushing toilets... everything that is typical in a home on a day to day basis.
Any help or advice you can provide would be GREATLY appreciated.