I have been getting a sewer gas odor in my bathroom. I noticed the odor outside and thought the odor was finding its way in so I bought a Sweet Aire vent cap (charcoal filter) and installed it on the roof stack. The odor outside is gone. I've narrowed down the source to the toilet in my master bathroom which is in a 3' x 5' room by itself. When the shower in my other bathroom is in use, the smell appears. When I flush this toilet, the smell(sometimes)appears. The toilet doesn't leak either above or below the floor. The toilet is brand new, called a Titan by Eljer. The toilet in my other bathroom is directly behind it on the other side of the wall. Both toilets operate properly except for the smell (from the one toilet.) The picture attached shows the drainwork from both toilets. The good toilet is in the top of the picture, the second toilet is the one that wye's into the main line. The vent stack goes vertical in the wall between the two toilets.