Plumbing Questions? Ask a Plumbing Expert.
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Sorry to hear about your problem.
It has to be a venting problem; air bubbles are a sure sign that the main vent pipe is partially clogged from an animal getting caught or a bird building a nest, snow/ ice, etc. This would effect proper draining as well. The vent sucks in air and replaces the displaced water, allowing it to drain properly; it can be compared to holding your thumb on the end of a drinking straw that is full of water; the water will stay in the straw, until you lift your thumb, allowing the air in. A high pressure nozzle, on the end of a water hose, can be used up on the roof to spray down the main vent pipe. This is effective at clearing blockages in the vent pipe only; often the vent pipe can be augered as well. See short video below for more information.
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Best of Luck, Brian