Why is my toilet gurgling?

What people usually report

A glug or bubbling from the bowl when a nearby sink or tub drains, when the washer empties, or on its own. Sometimes the water level in the bowl rises and falls, or the toilet flushes weakly.

What official sources say the causes can include

• A blocked plumbing vent. The roof vent lets gases from the sewer or septic system out. When it is blocked, water can be pulled from the traps, and a gurgling or poorly flushing toilet may be the first sign. Snow can block the vent stack (North Dakota State University Extension), and in cold weather moisture in sewer gas can freeze at the top of the vent (North Dakota State University Extension). Wisconsin’s health department also lists a blocked roof vent as a way sewer gas gets into a home (Wisconsin Department of Health Services).
• A blockage in the drain or main line. Slow draining or gurgling in sinks, showers, or toilets is a sign of a blockage, and all drains backing up at once points to the main sewer line rather than one fixture (Town of Simsbury, CT, Water Pollution Control).
• A septic system problem. On septic, EPA lists gurgling sounds alongside slow drains, backups, and sewage odors near the tank or drainfield (U.S. EPA).

Who is responsible for which pipe

On a public sewer, the pipes inside a building and the lateral from the building to the sewer main are the property owner’s to maintain, and lateral repairs are licensed-plumber work. Sewage in the street or outside the house is a public main problem and should be reported to the town or sewer authority (Town of Simsbury, CT, Water Pollution Control). Local rules vary, so check with your own sewer utility.

How to find out

1. One fixture or several? Run the sink and tub nearest the toilet, then fixtures on other floors, and note which ones gurgle or drain slowly. Simsbury says all drains backing up at once points to the main sewer line rather than a single fixture (Town of Simsbury, CT, Water Pollution Control).
2. Look outside in winter. If a frost-capped vent is possible, you may see snow piled over the vent pipe on the roof. NDSU describes vent insulation and taller insulated vents as longer-term fixes (North Dakota State University Extension). Leave roof work to a professional.
3. On septic, check when the tank was last pumped. EPA recommends inspection every 1 to 3 years and pumping every 3 to 5 (U.S. EPA).

A main-line clog is drain-cleaning work; see what drain cleaning costs. A running rather than gurgling toilet is a different problem: toilet keeps running.