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Fix a septic system that backs up

We'll check for clogs, the septic pump, and tank level—or tell you when to call a septic professional.

Troubleshooting · Home plumbing
15–45 min
What you'll need
  • Plunger (flange for toilet, cup for sink)
  • Drain snake (optional, for main line)
  • Bucket and towels
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Steps

Goal: Stop water use, check for clogs, and verify the septic pump if you have one.

  • Stop using water immediately. Do not flush or run sinks.
  • Determine if one fixture or the whole house is affected. Single fixture—try a plunger. Whole house—check the main line and pump.
  • Good: Single fixture—try Check single fixture. Bad: Whole house—check Main line and Pump.

Check single fixture

Goal: Clear a local clog at one fixture.

  • Use a flange plunger for a toilet, cup plunger for a sink. Pump firmly 10–15 times.
  • Good: Clog clears. Bad: Still backed up—check main line or call a septic professional.

Check main line

Goal: See the backup level at the main cleanout.

  • Locate the main line cleanout. Remove the cap carefully. If sewage is at the top, the main line or septic tank is backed up.
  • Good: You know the level. Bad: Call a septic professional for pumping or inspection.

Check pump

Goal: Verify the septic pump runs and the float switch works.

  • Listen for the pump. If it is off, check the breaker and float. Gently move the float to see if the pump starts.
  • Good: Pump runs. Bad: Pump will not run—call a septic professional.

When to get help

Call a septic professional if:

  • Water backs up from multiple fixtures.
  • The tank is full and needs pumping.
  • The pump will not run or the float is stuck.
  • You smell sewage.

Do not use chemical drain openers—they damage the septic system.

Verification

  • No backup from fixtures or cleanout.
  • Pump runs when the tank level rises (if you have a pump).

Escalation ladder

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

  1. Stop water use Do not flush or run water—prevents more backup.
  2. Check single fixture Try plunger or snake at one fixture if only that one is affected.
  3. Check main line Inspect main line cleanout to see backup level.
  4. Check pump If you have a pump, verify it runs and the float works.
  5. Call septic pro Whole-house backup, tank full, pump failed, or drainfield issue—call a septic professional.

What to capture if you need help

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

  • Single fixture or whole house?
  • Main line cleanout level
  • Whether the pump runs (if applicable)
  • Float switch condition
  • Steps already tried

Is only one fixture backing up?

Single fixture suggests a local clog. Whole house suggests main line or septic tank.

Check which fixtures are affected. One fixture: try plunger or snake at that fixture. Multiple fixtures: main line or septic tank—check main cleanout and pump. Do not use chemical drain openers.

Yes No (whole house)

You can change your answer later.

Did the plunger or snake clear the clog?

Use a flange plunger for toilet, cup plunger for sink.

Try a plunger or drain snake at the affected fixture. Good: clog cleared—backup stops. Bad: still backed up—check main line or call a septic professional.

Yes No

You can change your answer later.

Backup is cleared

The clog is cleared. Use water sparingly for a few hours. If backup returns, the main line or septic tank may need attention—call a septic professional.

Done

Do you have a septic pump?

Pumped systems need the pump to move effluent to the drainfield. If the pump fails, the tank fills and backs up.

If you have a septic pump, check that it runs. Listen for the motor. Check the float switch. If the pump is off, the tank may be full—call a septic professional to pump and inspect.

Yes (have pump) No (gravity system)

You can change your answer later.

Is the pump running?

If the pump is off, the float may be stuck or the pump may have failed.

Listen for the pump. If it is off, check the circuit breaker and float. Gently move the float to see if the pump starts. Do not reach into the tank. If the pump will not run, call a septic professional.

Yes No

You can change your answer later.

Call a septic professional

Call a septic professional if: whole-house backup, tank is full, pump will not run, float is stuck, or you smell sewage. Tank pumping and drainfield work require a licensed pro. Do not use chemical drain openers.

Done

Reviewed by Blackbox Atlas

Frequently asked questions

Why would a septic system back up?
Common causes: a clog in the main line, a full septic tank that needs pumping, a failed or clogged pump (if you have one), or a blocked or failing drainfield. A single fixture backup may be a local clog; whole-house backup suggests tank or drainfield.
Can I fix a septic backup myself?
You can check for clogs in the main line and at fixtures. If you have a pump, you can check that it runs. Tank pumping and drainfield issues require a septic professional. Do not use chemical drain openers—they harm the septic system.
When should I call a septic professional?
Call a septic professional if: water backs up from multiple fixtures, the tank is full (pump-out needed), the pump is not running or the float is stuck, or you smell sewage. Tank and drainfield work require a licensed pro.

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