Many years ago in New Jersey they had a problem with the sewer in a fancy new office building that was only a year or so old. Turns out they had got the sewer pipes all the way out to within 20 feet of the main line during early construction, but for what ever reason were supposed to not connect until the project was near the end. Except they forgot to make the connection!
I don’t recall if it was a year or not, but I do know I was surprised at how long it took to fill up the sewer pipes to the point of not flushing and backing up into the building!