Why is the Toilet Bubbling?
If you have air bubbles that rise up through your toilet bowl (except when it flushes) or notice the water level rising and falling, you probably have a clogged or improperly vented toilet. This toilet bubbling problem is especially true when you have an appliance like a clothes washer nearby. Your drain plumbing line is gasping for air.
If you suspect it’s just a simple toilet clog, here’s how to unclog it.
Why is the water level rising and falling?
Other explanations for toilet water levels rising and falling are that a waste pipe could be pitched incorrectly, which can make the water settle to a new level or there is a hairline crack in the porcelain in the trap that is causing a slow leak. But it’s usually the air vent that causes the water level to rise and fall.
How drain plumbing works
When you pour liquid from a can, you’ll notice that it doesn’t flow evenly unless you have a second opening for air. The same holds true for plumbing vent pipe. As water goes down a drain, air is needed to equalize the pressure in the drain line.
This is the purpose of a venting system. If the drain lines in your home have poor venting (as in Figure A, for example), water rushing down the drains will pull water from nearby P-traps. The drain in the toilet bowl is basically a P-trap. If the problem just started, it’s probably a blocked drain or plumbing vent pipe that needs to be “snaked” out. And since the water in the toilet is dropping and gurgling, it’s likely that the problem is near that area.
Unfortunately, a clogged or missing vent is tough to fix, since it usually requires breaking into the walls to examine the drain system. Unless you have plumbing experience, this project is best left to a professional.
Figure A: Common Example of Poorly Vented Drains
Bathroom plumbing venting in this system is missing, or the vents don’t open to “free” air.