In the summer my downstairs toilet smells awful, like sewer, and in the winter the overflow lines for my airconditioning and water heater smell like mold. (they are located in garage) Any ideas about what could possibly be happening? Thanks

That over flow line is actually a condensate drain line and it can easily have mold growing in the pan below the A coil. Periodic bleaching should eliminate that issue. Now the toilet, does the toilet maintain a full bowl of water all summer or does it ever evaporate dry? Could also be a bad wax ring but that would be year round pretty much.

Thank you. The water level doesn't see to be any different-- I'm home all day most days so, it doesn't really have a chance to get low since I'm flushing the toilet several times a day. There are days when it doesn't smell at all--like today. The overflow lines only smell in the winter and I have poured bleach in those drains but it doesn' t stop the smell from coming through those lines in the winter--- in the summer there is absolutely no smell at all--- It is a really mystery.