Why Are My Drains Gurgling?

What it usually looks like

• A sink or tub makes a glug-glug sound as it drains or just after it finishes
• The toilet bubbles or its water level drops when another fixture drains
• Gurgling from a floor drain or shower when the washing machine empties
• A sewer smell shows up with the gurgle, especially in the morning
• Drains have gotten slower over several weeks
• The gurgling is worse after heavy rain

Likely causes, most common first

1. A partial blockage in the main drain or sewer

   When the main line is narrowed by roots, grease or sludge, water from a large discharge like a toilet flush or a draining tub has to push past the restriction. That creates suction behind it, and the easiest place to pull air from is the nearest trap. The toilet burps, the shower gurgles. This is the cause to rule out first because it only gets worse.

2. A blocked or undersized vent

   Every drain needs a vent to the roof so air can follow the water down. Leaves, a bird's nest, frost or a collapsed vent pipe in the attic will starve the system of air, and traps get siphoned as fixtures drain. A vent problem gurgles even when the drain itself is clean.

3. A clog in the fixture's own trap or branch

   Hair and soap in a tub trap, or grease in a kitchen branch, narrow the pipe right at the fixture. The gurgle is local and the fixture is slow. Clearing that one line solves it.

4. A full or failing septic tank

   On a septic home, a full tank or a plugged outlet baffle backs water up into the main line, and every fixture in the house starts to gurgle. Heavy rain saturating a drainfield produces the same symptom. A cable cannot fix a full tank.

5. An air admittance valve that has failed

   Some remodeled kitchens and island sinks use a small spring-loaded air admittance valve under the cabinet instead of a vent to the roof. Those valves stick shut after a few years, and the sink gurgles every time it drains.

6. A trap that has lost its water seal

   A floor drain or guest bathroom that is rarely used can have its trap evaporate. Air moves freely through it, and you hear it as gurgling or bubbling from a neighboring fixture, along with a sewer smell.

Safe things to check yourself first

• Note which fixture gurgles and what triggers it; a toilet that bubbles when the tub drains is a main line sign
• Fill the gurgling sink or tub and let it drain while you listen; slow drainage points to a local clog
• Pour a gallon of water down any rarely used floor drain or shower to refill its trap
• Look at the roof vent from the ground for visible debris, or at least confirm nothing has fallen onto it
• On a septic home, check when the tank was last pumped
• Stop using chemical drain cleaners; they do not help a gurgle and they make the pipe hazardous for whoever opens it next

How we diagnose and fix it

• Run water at several fixtures while listening at the others to pinpoint whether the air is coming through a branch, the main, or the vent
• Cable the main line from the cleanout and then run a camera to see what caused the restriction
• Clear a blocked roof vent from above, or trace a vent that was disconnected or crushed in the attic
• Replace stuck air admittance valves or add proper venting where a remodel left it out
• Hydro jet lines that are coated with grease or scale rather than just blocked at one point
• On septic homes, confirm the tank level and refer you to a pumper when the tank is the issue, since we do not pump tanks

Questions people ask