Gurgling Drains and Backups: Signs of a Main Line Clog

Gurgling drains and backups in more than one fixture are common signs of a main sewer line clog. Likely signs include a toilet that gurgles when a sink drains, water rising in the tub when you flush, and several slow drains at once. If sewage backs up, stop using water, keep people and pets away, and call a pro.

What should you do first if sewage is backing up?

If dirty water or sewage is coming up into a tub, shower, floor drain or toilet, start here.

1. Stop using water. Don't flush, run sinks, start the dishwasher or do laundry. Every gallon you send down has to go somewhere, and with a main line clog, it often comes up at the lowest drain in the house.
2. Keep children and pets away from the area until cleanup is done (CDC).
3. Protect yourself if you must touch it. The CDC says to wear rubber boots, rubber gloves and goggles if sewage is involved, and to wash with soap and water afterward (CDC).
4. Stay clear of water near electricity. If sewage or water is spreading toward outlets, cords or appliances, don't touch them while standing in it. The CDC says never to turn power on or off while standing in water (CDC).
5. Don't open the sewer cleanout yourself. A cleanout is a capped pipe that gives access to the main line. If the line is backed up, removing the cap can release sewage under pressure.
6. Call a plumber or drain company. A backup affecting several drains is not a plunger job.

For cleanup, the EPA suggests calling a professional who has experience with buildings damaged by sewage or other contaminated water (EPA).

What are the signs of a main sewer line clog?

The main sewer line carries all the wastewater from your house to the city sewer or your septic system. When it clogs, the symptoms show up in more than one place. Fixr lists these signs (Fixr):

• gurgling sounds from the toilet;
• water bubbling up in the shower or tub when the washing machine or dishwasher runs;
• water backing up in the shower when the toilet is flushed;
• several fixtures draining slowly, or standing water in several places;
• sewage coming up into a sink or tub;
• water backing up out of a cleanout pipe, which Fixr calls a serious blockage;
• a foul smell;
• soggy patches or dips in the yard over the sewer line.

The key pattern is more than one fixture affected at the same time, especially the lowest ones in the house. A single slow sink is usually a clog in that sink's own drain.

Why do drains gurgle?

Gurgling is the sound of air being pulled through water in a drain trap. Drains need a steady flow of air to work. When water can't move freely, it pulls air from wherever it can find it, including through other fixtures. Common reasons include:

• A clog in the main line. Water from one fixture backs up and pushes air through others, which is why a toilet may gurgle when the washing machine drains.
• A clog in a branch line. If only the fixtures in one bathroom gurgle, the clog may be in the line that serves that bathroom, not the main.
• A blocked plumbing vent. Every plumbing system has vent pipes that run up through the roof. This Old House says ice, snow or debris can block a vent, and a blocked vent can pull water out of a toilet's trap, letting sewer gas in (This Old House). Don't climb on the roof to check. A pro can clear it.

What causes a main sewer line clog?

Fixr lists these as the common causes (Fixr), roughly from the most everyday to the most serious:

• Grease, oil and food. Grease poured down the kitchen sink cools and sticks to pipe walls, catching everything that comes after it.
• Paper and flushed items. Thick paper, wipes and sanitary products don't break down the way toilet paper does.
• Tree roots. Roots grow into small cracks and joints in the line, then catch debris.
• Aging pipes. Fixr notes older clay or cast iron pipes deteriorate and eventually crack.
• A sagging pipe, or "belly." When the soil under a section of pipe settles, the pipe sags and collects waste.
• A broken line. A cracked or broken section can block flow entirely.

The first two are usually cleared with a cable or water jetting. Roots, sags and breaks can mean a repair to the line itself.

What can you safely check yourself?

Some checks help you and the pro understand the problem, without exposing you to sewage.

• Which drains are affected? Note every fixture that's slow, gurgling or backing up, and which floor it's on. Lowest-floor drains backing up first is a classic main line sign.
• Does running one fixture affect another? If running the washing machine makes the tub fill up, write that down.
• Is it just one drain? If only one sink or tub is slow and nothing else gurgles, a plunger or the fixture's trap is the usual place to start. See the cost section below for typical drain cleaning prices.
• Do you know where your cleanout is? Fixr says cleanouts are often in the yard near the street, and that some older homes don't have one (Fixr). Knowing where it is helps the pro. Don't open it during a backup.
• Is there a smell from a drain you rarely use? A sewer smell alone, without slow drains, can be a dry trap. This Old House says traps in floor drains that rarely get water can dry out and let sewer gas through (This Old House).

What to skip: Hold off on chemical drain cleaners in a backed-up line. They rarely reach a main line clog, and the pro will be working in that water. If you've already used one, tell them.

Can you snake the main line yourself?

Some homeowners do rent a sewer snake. Fixr lists a sewer snake rental at about $50 per day (Fixr). But a main line job is different from clearing a sink:

• You'd be working at the cleanout, often with sewage in the line.
• A powered snake can catch and twist, which can injure hands and arms if you haven't used one before.
• A snake can open a hole through the clog without telling you why it happened, so roots or a broken pipe can go unnoticed.

If sewage is already backing up, it's safer to let a pro handle it, and to ask for a camera inspection so you know what caused the clog.

What if you have a septic system?

If your home uses a septic tank instead of a city sewer, backups and gurgling can also come from the tank itself or the drain field, not just the pipe. A full tank can cause the same symptoms as a clogged line. Tell the pro you're on septic, and when the tank was last pumped. Fixr lists septic tank cleaning at $400 to $1,000 (Fixr).

When should you call a pro?

Call a pro if:

• sewage or dirty water is coming up into a tub, shower or floor drain;
• more than one drain is slow or gurgling;
• toilets gurgle or bubble when other fixtures run;
• the clog keeps coming back after you clear it;
• there's a sewage smell that doesn't go away;
• you see soggy ground or sinkholes over the sewer line.

Sewer gas is also worth taking seriously. This Old House says it can cause headaches, dizziness, nausea and drowsiness (This Old House).

If you're not sure how serious it is, Bellwick's free check asks a few questions about which drains are affected and shows the likely causes, typical costs and questions to ask. Check my plumbing.

What will a pro check?

A plumber or drain company will usually:

• ask which fixtures are affected and when it started;
• find the cleanout, or the best access point to the main line;
• run a cable (snake or auger) or a water jetter through the line;
• recommend a camera inspection to see what caused the clog, especially if it comes back or roots are suspected;
• tell you whether the line itself has a break, sag or root problem that needs repair.

A camera inspection is worth asking about if this isn't the first backup. It shows whether the line is clear or damaged, so you aren't paying to clear the same clog over and over.

How much does it cost to clear a main sewer line?

As of 2026, here are national ranges from Fixr. Local prices vary.

• Unclogging a main sewer line: $350 to $650, with a national average of $475 (Fixr).
• Snake or auger: $100 to $500 (Fixr).
• Rodding: $150 to $600 (Fixr).
• Hydro jetting: $350 to $600 (Fixr).
• Camera inspection: $100 to $800 (Fixr).
• Tree root removal: $100 to $800 (Fixr).
• A sagging (bellied) line: $1,500 to $3,000 (Fixr).
• A broken line: $1,500 to $3,000 (Fixr).
• Sewer pipe repair: $50 to $250 per linear foot (Fixr).
• Installing a cleanout where there isn't one: $600 to $2,000 (Fixr).
• Sewage backup cleanup: $2,000 to $10,000 (Fixr).
• Emergency off-hours charge: $50 to $100 (Fixr).

For a single slow drain, standard drain cleaning runs $150 to $300 (Fixr).

Fixr also warns that very low advertised prices, like $69 or $99, can be a red flag (Fixr). Ask what the price includes before work starts. For a fuller breakdown, see our guide to drain and sewer line cleaning costs.

Should you clear the line or repair it?

Clearing is usually the first step. It gets water flowing again. But if the clog comes back, the cause may be in the pipe itself.

Clearing alone usually makes sense when:

• it's the first backup in a long time;
• a camera shows grease, paper or a foreign object, with no damage to the pipe.

A repair is worth discussing when:

• the same clog keeps coming back;
• a camera shows roots growing through joints, a crack, a sag or a collapse;
• the yard over the line is soggy or sinking.

Ask the pro to show you the camera footage, or send it to you, before you agree to a repair.

Questions to ask before you approve the work

• Where do you think the clog is, and how will you confirm it?
• Will you use a camera to see what's causing it?
• What does the price include: clearing, camera, and cleanup?
• Is there an emergency or after-hours fee?
• Can I get the price in writing before you start?
• If the line is damaged, can you show me the footage?
• What can I do to keep this from happening again?
• Is your work guaranteed, and for how long?
• Are you licensed and insured for this work where I live?

How can you prevent another backup?

• Keep grease out of the sink. Let it cool and throw it in the trash.
• Flush only toilet paper. Thick paper products and sanitary products are on Fixr's list of causes (Fixr).
• Use drain screens in showers and tubs to catch hair.
• Know where your cleanout is, so a pro can reach the line quickly.
• Ask about regular cleaning if you have older pipes or big trees near the line.
• Run water into rarely used drains now and then, so traps don't dry out.

If you notice a sewer smell without slow drains, the cause may be a dry trap, a vent or a seal rather than a clog. And if water seems to be leaking from a supply pipe rather than backing up from a drain, see our guide to a burst pipe.

The bottom line

When more than one drain is slow or gurgling, or water comes up in the tub when you flush, a main line clog is a likely cause. Stop using water, keep people and pets away from any sewage, and don't open the cleanout during a backup. A pro can clear the line and use a camera to see what caused it, which tells you whether you're dealing with a one-time clog or a pipe that needs repair.

When you're ready, check my plumbing to see the likely causes and questions to ask.