How to Install a Plastic Septic Tank

Stephen Hasty

Septic tanks made of lightweight plastic are easy to transport and move, but plastic tanks also can deform when installed in unstable soils and float in saturated soils without proper ballast. Plastic pump chambers low on liquid are especially susceptible to flotation in saturated soils.

Plastic septic tanks are a lightweight alternative to concrete.

Plastic tanks are a useful option when locations are not reachable by concrete septic tank trucks or the area is sensitive to heavy equipment. Professionals familiar with the long-term issues faced by homeowners with plastic septic tanks can offer advice on how to prevent future problems.

  1. Excavate where the new plastic tank will be located to the dimensions supplied by the tank's manufacturer using an excavator. Check elevations with a laser level.

  2. Thread a chain through the lifting eyes molded to the tank, and attach the chain to the excavator's bucket.

  3. Lift the tank with the excavator and lower it into the hole. Release the tank from the excavator. Lifting any material or equipment off the ground is dangerous. Keep all work crew at a safe distance.

  4. Thread a chain through the lifting eyes on the concrete weights, and attach the chain to the excavator.

  5. Lower the concrete weights and place them on either side of the tank.

  6. Thread the cable through the lifting eye on the concrete weight, drape the cable over the top of the plastic tank and thread the cable through the lifting eyes on the other concrete weight.

  7. Thread the cable through the cable clamps and use a socket wrench to tighten the bolts, securing the clamp to the cable.

  8. Insert a garden hose into the tank and fill the tank with water. At the same time, use the excavator to backfill the hole with soil. Compact the soil with a vibratory compactor in 6- to 8-inch increments.