My downstairs toilet is bubbling when I let out my bath water from upstairs. It flushes fine but the bubbling is a concern and water over flowed from the toilet when I let the bath water out this last time. All the other toilets in my house are working great. Please help me.

The first thing I would try is snaking the lavatory roof vent. Put out enough snake to reach the base and 20 feet more. If that don't get it I would pull the toilet and snake the line from there. Good luck, Tom