you might want to have your sewer line checked out to see if there is a blockage. try flushing a toilet or run a sink (go to the lowest point in your plumbing system, like a laundry sink in the basement) and see if the water drains slowly. I recently had a similar problem where I noticed my dishwasher wasn't draining & a week later my toilet (lowest point in my plumbing system) overflowed with raw sewage. There was a blockage in the sewer line between my house and the road.