Keep Mosquitoes Out of Your Septic Tank

What to know

  • Mosquitoes can spread germs that make people sick.
  • Just one septic tank can produce thousands of mosquitoes.
  • Mosquitoes get inside broken or unsealed septic tanks and lay eggs.
  • After they hatch and grow, thousands of adult mosquitoes fly out of the broken or cracked septic tank each day.
An adult Aedes aegypti mosquito emerges from water. Four pupae are adjacent.

Mosquitoes and septic tanks

Mosquitoes may be laying eggs inside your septic tank if it is

  • Open or unsealed
  • Broken with cracks or spaces between the blocks
  • Missing a ventilation pipe screen cover
Hundreds of mosquitoes line a wall of a septic tank.
Mosquitoes rest on the walls of septic tanks.
A broken cement septic tank cover with a "no" symbol.
Repair or replace broken septic tank covers.
An uncovered septic tank ventilation pipe sticks above the groun.
Cover septic tank ventilation pipes.

Inspect and repair your septic tank

Check local regulations before repairing a septic tank on your own. You can work with a licensed septic tank installer to

  • Seal the septic tank.
  • Repair cracks or gaps in the exterior walls of the septic tank using cement or expanding foam used for home insulation projects.
    • Look for a product that is made to fill big gaps and is water resistant.
    • Follow directions on the product label.
  • Cover vent or plumbing pipe openings using mesh with holes smaller than a mosquito.
  • Fill abandoned or unused septic tanks with dirt or gravel.
Septic tank ventilation pipe with a mesh cover. A checkmark is added.
Septic tank ventilation pipe covered with screen mesh.
A septic tank with a concrete cover. A check mark is added.
Septic tank covered with a concrete cover.
A septic tank with a PVC cap. A check mark is added.
Septic tank sealed with a PVC cap.

Fact sheets

Keep Mosquitoes Out of Your Septic Tank