Ever since tapping into our towns new sewer system, we have had problems with our toilet in the downstairs bathroom. Directly above this toilet is the toilet in our other bathroom. When the upstairs toilet is flushed, the downstairs toilet bubbles (large bubbles). I suspect the system is not properly vented; the only vent pipe for the entire house is a small (approx 1.5") vent pipe through the roof. I would like to properly vent the system but I need more detailed info on how to do it. Can anyone recommend a specific book?