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How to fix a leaky septic tank

Septic tanks can leak in several places, including the inlet pipe and outlet pipe, as well as the manhole riser. Water and waste water can flow in or out of the tank. Excess water leaking into septic tanks hydraulically overloads tanks and drain-fields, leading to system failure. Waste water leaking out of a septic tank pollutes groundwater and may surface. Surfacing septic tank waste water causes bad odours and potential human contact.

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  1. Schedule a time for the underground utilities to be marked. Private utilities may not be marked by the public utility companies and will have to be marked by a private utility locater.

  2. Schedule the tank to be pumped by a septic tank cleaning company.

  3. Lower a mirror into the tank and shine a flashlight on it. Look around the tank using the mirror to determine where the leaking is occurring.

  4. Remove the soil covering the tank's riser and inlet and outlet pipes with the excavator. Excavate to at least 1 foot lower than the pipes for room to work. Be careful when removing soil from the tank. Applying too much pressure can break a septic tank. Be sure to hand shovel directly over the septic tank and pipes.

  5. Remove the existing tar sealant from the void between the pipe and the tank.

  6. Clean the area with a wire brush and trowel to remove any remaining sealant, dirt and debris.

  7. Allow the area to thoroughly dry.

  8. Heat the new tar sealant by leaving it in direct sunlight for 15 minutes.

  9. Apply the sealant to the void between the pipe and the tank. Press firmly into place using a trowel.

  10. Test the area with water spray to see if the leaks reappear.

  11. Replace the soil, taking care not to disturb the newly sealed pipes.

  12. Remove the manhole covers from the septic tank risers.

  13. Remove the concrete risers by placing a bar lever at the seam of the riser and the tank and prying up. Considerable pressure may be needed to break the seal.

  14. Clean the mating surfaces of the risers and the tank with a wire brush and trowel, completely removing any remaining sealant, dirt and debris.

  15. Allow the concrete to thoroughly dry.

  16. Heat the new tar sealant by leaving it in direct sunlight for 15 minutes.

  17. Apply the sealant to the top of the septic tank where the manhole riser will be placed. Lower the riser on top of the mastic and press down firmly to bond the materials.

  18. Replace the manhole cover over the riser to keep out soil during backfilling and to add weight to the riser for better sealant adhesion.

  19. Replace the soil, taking care not to disturb the newly installed riser.

  20. Tip

    Stained concrete around the riser or the outlet and inlet pipe openings is a sign of leaks. Some states have a one-call system for utility locates. These systems will locate all public utility providers in the area and have them mark the excavation site. Use rubber gloves when handling the tar sealant.

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Things You'll Need

  • Septic tank tar sealant
  • Trowel
  • Rubber gloves
  • Mirror
  • Flashlight
  • Excavator
  • Wire brush
  • Bar lever
  • Shovel

About the Author

Stephen Hasty started writing in 2009. Covering technical articles and newsletters, his work has appeared in "The Kennebec Valley Plumbing Newsletter" and "Maine Leasing." Hasty holds a bachelor's degree from Saint Cloud State University, a real estate sales agent license and a master plumber license from the state of Maine.

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