What causes bubbles to form in a toilet?


Quick Answer

Air bubbles that come up into a toilet bowl when it is not being flushed are a sign of a clog or poor venting in the toilet. The drain line from the toilet is sending bubbles up as a sign that it needs air.

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Full Answer

Opening a can of broth or evaporated soup on just one side leads to an uneven flow, but adding a second opening to allow air in causes the flow to even out, and the same principle applies to plumbing. When water goes down a drain, air is necessary to maintain equalized pressure throughout the system.

A bubbling toilet is a sign that the drain lines in that building have poor venting. As water runs down the drain, poor venting causes the drains to yank water from P-traps along the way, and the toilet bowl drain is a type of P-trap. The solution is to run a plumber's snake into a blocked vent or drain. The louder the toilet is gurgling, and the more bubbles it is producing, the more likely it is that the problem is close to that toilet. The best way to fix the problem is to call a plumber, as the fix generally requires going behind the walls to give the drainage system a close inspection.

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