Hi Chris:
You have described my problem exactly, and your idea of the smoke does not seem all that eccentric at all, but now you have to explain a few things to me because as far as plumbing is concerned I know as much as the average housewife (although keen to learn) firstly I should have pipes that take dirty water away excluding toilet, then big pipe for toilet waste and thirdly water from rain that also should not mix.
Now, at the corner of the room and the house OUTSIDE (the room in question used to be a garage) I have the pipe for rain water that has a concrete box (hole ) with a lid which you can open and see two tubes going at angule of 90 degrees (the corner of the house. The smell is along the wall from were 1) the rain pipe runs paralel to meet the other that takes the water from the other half of the roof, 2) the MAIN toilet pipe which has a lid on the wall if you had a big blockage. I do not see anywhere the 3rd one (dirty water excluding toilet, so if I wanted to put the smoke through , through which one should I do that from? and can you explain how to make and conduct smoke in a particular direction?, at one point we thought the smell came in drafts through the wall at the base of it are the pipes. thanks,
SUZETTE