: I have two bathrooms - one downstairs, directly below the one up stairs. Every time I flush the up stairs toilet, my downstairs toilet bubbles like something you'd see at Yellowstone National Park. The same thing happens (only smaller bubbles and less noticeable) when the up stairs sink and shower drains. For example, after I'm finished shaving (upstairs), I'll pull the plug in the sink and wait, and wait, and wait for the water to go down. As the water slowly drains, I'll go downstairs - and sure enough the toilet is bubbling. A lot of people have told me it's a vent problem. What do you think?
I think there is a restriction in the drain where you're shaving and a separate problem in which the drain pipe downstream of the lower level toilet is partially clogged.
The main drain and the lavatory basin drain upstairs should be checked and snaked/cleaned as needed.