Hi hoping someone can help. We have an ensue bathroom that was added about 20 years ago. The toilet flushes into a separate soil pipe which runs into a drain at the side of the house. The toilet has not flushing well for some time and we have stopped using it. However sometimes waste comes back into the toilet, and the smell is terrible. The en suite is on the first floor so I am worried. What might be causing this? I have had a plumber round who didn't know, he checked the manholes outside and could see no sign of obstructions in the drain.