How to Clear a Main Sewer Line Clog

Signs of a Main Sewer Line Clog

• Multiple drains back up at once: If the kitchen sink, shower, and toilet all drain slowly or back up simultaneously, the problem is downstream of where those lines converge — your main sewer line.
• Sewage at the cleanout: Remove the cap on your sewer cleanout (usually a white PVC or cast iron cap in the yard or basement). If you see standing water or sewage, the main line is blocked between the cleanout and the street.
• Toilet bubbles when another fixture drains: Flushing a toilet causes the tub to gurgle, or running the washing machine causes the toilet to bubble. This indicates trapped air from a downstream blockage.
• Sewage odor from drains or yard: A persistent sewer smell — especially near the cleanout or in low-lying areas of the yard — signals a clog or break in the main line.

DIY: Using a Drain Auger Through the Cleanout

1. Locate your sewer cleanout. It's a capped pipe (typically 4-inch diameter) at ground level in the yard, in the basement, or in a crawlspace. Some homes have two — one near the house and one near the property line.
2. Rent a motorized drain auger. Home improvement stores rent 50–100 ft motorized sewer augers for $30–$60/day. You need a machine with at least 75 ft of cable and a cutting head designed for 4-inch pipe.
3. Remove the cleanout cap carefully. If the line is full, sewage will flow out when you open it. Stand to the side, use a wrench, and have towels and a bucket ready.
4. Feed the auger cable into the cleanout toward the street. Run the machine at moderate speed. When you hit the clog, you'll feel resistance. Let the cutting head work through it — don't force the cable, which can kink or break.
5. Run water to verify flow. Once the cable moves freely, pull it out and run a garden hose into the cleanout for 5 minutes. If water flows freely to the street, the clog is cleared.

When to Call a Professional

Call a licensed plumber if:

• The DIY auger can't break through the clog (likely tree roots or a collapsed pipe)
• The clog returns within weeks (root intrusion or a bellied/broken pipe)
• You see sewage backing up into the home — this is a health hazard requiring immediate professional response
• Your home has cast iron or clay sewer pipe — aggressive augering can damage aged pipe

A plumber will typically start with a camera inspection ($100–$300) to diagnose the cause, then use a professional auger or hydro-jet (1,500–4,000 PSI) to clear the line. Camera inspection pays for itself by preventing unnecessary digging or repeat service calls.

Common Causes and Long-Term Solutions

• Tree roots: Roots enter through pipe joints and grow until they block flow. After clearing, treat with copper sulfate or foaming root killer every 6–12 months. For severe intrusion, consider pipe lining ($80–$250 per linear foot) to seal joints permanently.
• Grease buildup: Cooking grease coats the pipe interior and hardens over time. Hydro-jetting is the only effective removal method. Prevent recurrence by never pouring grease down drains.
• Collapsed or bellied pipe: Sections of old clay or cast iron pipe that sag or collapse require excavation and replacement ($50–$250 per linear foot) or trenchless pipe lining.