Daughter has developed a bad sewage type smell in the kitchen. I've replaced all the sink drain plumbing, but the smell is still there. This weekend I spotted a hole in the cast iron soil stack (as shown approx on image) behind the pipe next to the wall. On inspection this was the same smell and there were a couple of chunks that were loose which I have removed. Obviously the stack will need replacing at some point, but my question really is could this be the source of the smell? How would it get from here through the wall and into the kitchen? The smell does not seem to be anywhere else in the house.