Fiberglass Septic Tank

About Fiberglass Septic Tanks

Fiberglass septic tanks are manufactured using a process called filament winding or hand layup, where layers of fiberglass cloth are saturated with polyester or vinyl ester resin and built up to the required wall thickness. The resulting tank is extremely strong for its weight, completely waterproof, and immune to all forms of chemical and biological corrosion. Fiberglass tanks are typically manufactured as one-piece seamless units, which eliminates the joint leakage issues that can affect multi-piece concrete tanks. The smooth interior surface resists sludge adhesion, making pumping more efficient and thorough. Fiberglass tanks have been in service since the 1960s with many early installations still functioning well, demonstrating the material's long-term durability in buried wastewater applications.

Available Sizes and Costs

The table below shows the available sizes for fiberglass septic tanks with estimated purchase costs and annualized costs based on the expected 30-year lifespan. The annualized cost divides the purchase price by the expected service life to show the true yearly cost of ownership, which is the most meaningful way to compare tank materials of different lifespans. Delivery, excavation, and installation labor are not included in these prices and typically add $1,000 to $3,000 to the total installed cost.

Advantages

• Lightweight construction makes transportation and installation easier in difficult access areas
• Completely resistant to rust, corrosion, and chemical deterioration from wastewater
• Will not crack from hydrogen sulfide gas exposure unlike concrete tanks
• One-piece seamless construction eliminates joint leaks and infiltration points
• Smooth interior walls reduce sludge buildup and make pumping more efficient
• Can be installed by hand in locations where crane access is not available

Disadvantages

• Higher purchase price per gallon compared to concrete and polyethylene options
• Lightweight construction requires anchoring in high water table areas to prevent flotation
• More susceptible to damage during delivery and installation from impacts and rough handling
• Limited availability in larger sizes above 1500 gallons in some markets
• Cannot be easily repaired if damaged during installation or by soil movement
• May shift or float out of position during heavy rain if not properly anchored

Installation Considerations

Fiberglass tanks can be placed by two to four workers without heavy equipment, making them ideal for sites with limited access. The excavation should be bedded with 6 inches of clean sand to protect the tank bottom from rocks. Backfill should be clean sand or pea gravel compacted in 6-inch lifts to provide uniform support. In high water table areas, the tank must be anchored with concrete deadmen or straps to prevent flotation when empty. The tank should be partially filled with water during backfilling to prevent deformation from external soil pressure.

Regardless of tank material, all installations must comply with state and local code requirements for setback distances from wells, property lines, buildings, and water bodies. A licensed installer familiar with local requirements should perform or supervise all tank placement and connection work. Post-installation inspection by the permitting authority is required before the tank can be backfilled and put into service. Keep accurate records of the tank location, size, material, and installation date for future maintenance reference and potential property sale disclosure requirements.

Frequently Asked Questions

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