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Fix a main drain that is clogged

We'll help you locate the cleanout, snake from there toward the street, and tell you when to call a plumber for tree roots or deep blockages.

Troubleshooting · Home plumbing
30–90 min
What you'll need
  • 25–50 foot drain snake or sewer auger
  • Wrench for cleanout cap
  • Bucket, towels, gloves
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Steps

Goal: Confirm multiple fixtures are affected, locate the cleanout, snake from there, or call a plumber when needed.

  • Check if the toilet, sinks, tub, or floor drain back up or drain slowly when you run water. If only one fixture is slow, the clog is likely in that branch—not the main.
  • Good: Two or more fixtures affected—main clog likely. Proceed to Locate cleanout.
  • Bad: Only one fixture slow—branch clog. See how-to-unclog-drain or the fixture-specific guide.

Locate cleanout

Goal: Find the main cleanout so you can snake from there.

  • The cleanout is a capped pipe, usually 3–4 inches in diameter, in the basement, crawl space, or near the foundation where the main line exits the house. It may have a square nut or hexagonal cap.
  • Good: You found the cleanout. Proceed to Snake from cleanout.
  • Bad: You cannot find it—call a plumber.

Snake from cleanout

Goal: Remove the cap, feed the snake toward the street, and work through the blockage.

  • Place towels and a bucket. Put on gloves. Remove the cleanout cap with a wrench (counterclockwise). Water or sewage may come out—that confirms a blockage downstream.
  • Insert the snake and feed it toward the street (or septic tank). Crank clockwise as you push. At resistance, keep cranking to bore through or hook the clog. Pull back slowly—debris on the tip confirms you reached the blockage.
  • Run the toilet, sinks, and tub. Check that all fixtures drain without backing up.
  • Good: Fixtures drain normally—clog cleared. Replace the cap. See Verification.
  • Bad: Snake cannot reach it, you hit roots, or backup continues—call a plumber.

When to get help

Call a plumber if:

  • You cannot locate the cleanout.
  • The snake cannot reach the blockage.
  • You pull back roots or heavy grease and backup continues.
  • Sewage backs up into the house.

Main-line work often needs a motorized auger or hydro-jetting.

Verification

  • All fixtures (toilet, sinks, tub, floor drain) drain normally when run.
  • No backup when you flush or run multiple fixtures at once.
  • Cleanout cap is replaced and does not leak.

Escalation ladder

Work from the device outward. Stop when the problem is fixed.

  1. Confirm symptom Verify multiple fixtures are affected; rule out a single-fixture clog.
  2. Locate cleanout Find the main cleanout in basement, crawl space, or near the foundation.
  3. Snake from cleanout Remove cap, feed snake toward street, work through the blockage.
  4. Call a plumber Snake cannot reach blockage, roots or heavy grease, sewage backup—call a pro.

What to capture if you need help

Before calling support or posting for help, have these ready. It speeds everything up.

  • Which fixtures are affected
  • Whether you located the cleanout
  • Snake length and type used
  • What you pulled back (roots, grease, debris)
  • Steps already tried

Do multiple fixtures back up or drain slowly?

Check toilet, sinks, tub, floor drain. If only one fixture is slow, the clog is likely in that branch.

Run the toilet, sinks, and tub. Good: two or more fixtures back up or drain slowly—main clog likely. Bad: only one fixture slow—branch clog; try that fixture first or see how-to-unclog-drain.

Yes No

You can change your answer later.

Can you locate the main cleanout?

The cleanout is a capped pipe, usually in the basement or near the foundation.

Look for a 3–4 inch capped pipe in the basement, crawl space, or near where the main exits the house. Good: you found it. Bad: cannot find it—call a plumber.

Yes No

You can change your answer later.

Did the snake clear the blockage?

Remove the cleanout cap, feed the snake toward the street, crank through the blockage.

Remove the cap, insert the snake, feed toward the street. Crank at resistance. Pull back—debris on the tip confirms you reached the clog. Run fixtures to test. Good: fixtures drain—clog cleared. Bad: snake cannot reach it, you hit roots, or backup continues—call a plumber.

Yes No

You can change your answer later.

Main drain cleared

All fixtures drain normally. Replace the cleanout cap. Avoid flushing wipes or grease to prevent future clogs.

Done

Call a plumber

Call a plumber if multiple fixtures back up and you cannot locate the cleanout, the snake cannot reach the blockage, you pull back roots or heavy grease and backup continues, or sewage backs up into the house. Main-line work often needs professional equipment.

Done

Reviewed by Blackbox Atlas

Frequently asked questions

What causes a main drain to clog?
Tree roots invading the pipe, grease buildup, or objects flushed down the toilet. Roots are common in older homes; grease accumulates over time. A main clog affects multiple fixtures.
Can I snake the main drain myself?
Yes, if you can access the cleanout and have a long enough snake (25–50 feet for most homes). Remove the cleanout cap, feed the snake toward the street, and crank through the blockage. Call a plumber if you cannot reach it or hit roots.
When should I call a plumber for a main drain clog?
Call a plumber if the snake cannot reach the blockage, you pull back roots or heavy grease, sewage backs up into the house, or you cannot locate the cleanout. Main-line work often needs professional equipment.

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