We live in an end of terrasse house with 2 manholes in the back garden. For the past year we have a smell of sewege in the house. It is not there at all times, sometimes it can be gone for a few days other days it will come a few times a day. It seems to me as it is coming up from our floor in the hallway and from the back of the kitchen sink. It comes at irregular times, not when we are using the water, so with no pattern what so ever! I have had 3 plumbers here and also the council but nobody seems to find anything. This is all very disheartning and I don't know what to do?