In our house we have an internal stench pipe that is boxed in, and last month started to notice a foul smell in the area of the pipe. After a lift of the closest manhole cover we found it to be backed up. so we rodded it thorugh and now it flows freely, and the smell dissapeared. However we can now at times still slightly smell the same smell. but this time all the manholes are clear and running free. Is there a possiblity of the stench pipe being broken or cracked and leaking slightly, perhaps at the bottom where it takes a bend ( under the floor) to run into the manhole, Is there any trick of the trade to test the stench pipe without damaging its boxing in etc ect, Thanks for any advice