Steel Septic Tank
About Steel Septic Tanks
Steel septic tanks were once common due to their low manufacturing cost and structural strength, but have largely fallen out of favor for new residential installations due to their susceptibility to corrosion and relatively short service life. Steel tanks corrode from both the inside, due to hydrogen sulfide gas and acidic wastewater, and the outside, due to soil moisture and chemical exposure. Even with protective coatings and cathodic protection systems, steel tanks typically develop significant corrosion within 15 to 20 years. The most dangerous failure mode of steel tanks is lid collapse, where the top of the tank corrodes to the point of being unable to support the weight of soil cover or a person walking above it, creating a serious fall hazard. Many states and counties have either banned new steel septic tank installations or strongly discourage them through building code provisions.
Available Sizes and Costs
The table below shows the available sizes for steel septic tanks with estimated purchase costs and annualized costs based on the expected 18-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.
| Size | Est. Tank Cost | Annualized Cost | Typical Use |
|---|---|---|---|
| 500 gal | $300 | $17/yr | 1-2 bedroom homes, small cabins |
| 750 gal | $450 | $25/yr | 1-2 bedroom homes, small cabins |
| 1,000 gal | $600 | $33/yr | 3 bedroom homes (most common) |
| 1,500 gal | $900 | $50/yr | 4-5 bedroom homes |
Advantages
- Lowest initial purchase cost per gallon of all tank materials
- Strong structural integrity resists soil pressure and vehicle loads when new
- Can be manufactured in custom sizes and configurations for unusual site requirements
- Widely available in agricultural supply markets and from metal fabricators
Disadvantages
- Shortest lifespan of any tank material at 15 to 20 years due to rust and corrosion
- Steel corrodes from both internal wastewater exposure and external soil moisture contact
- Corroded tank lids can collapse under the weight of a person walking over them creating a safety hazard
- Most jurisdictions have banned or discouraged new steel tank installations due to failure rates
- Requires cathodic protection or coatings that add ongoing maintenance costs
- Replacement is virtually guaranteed within 20 years making lifetime cost higher than concrete
- Rusted baffles fail before the tank itself causing drain field damage from solids carryover
Installation Considerations
Steel tank installation is similar to concrete but with additional corrosion protection steps. Apply bituminous coating to the exterior before burial. Install a sacrificial anode cathodic protection system to slow corrosion. Ensure all seams and joints are fully welded and sealed. Steel tanks should never be installed in acidic soils or high water table areas without extensive corrosion mitigation. Regular inspection of the tank lid and access ports is critical for safety, as corroded lids can collapse without warning.
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
How long does a steel septic tank last?
A properly installed and maintained steel septic tank typically lasts 18 years or more. Steel tanks have the shortest lifespan due to inevitable corrosion from both internal and external surfaces. Regular inspection is critical to detect thinning walls before catastrophic failure.
How much does a 1,000 gal steel septic tank cost?
A 1,000-gallon steel septic tank costs approximately $600 for the tank itself. This does not include delivery (typically $200-$500), installation labor ($500-$2,000), or excavation costs. Total installed cost for the tank component alone is typically $1,300 to $3,100 depending on site conditions and local labor rates.
Is steel a good choice for a septic tank?
Steel is generally not recommended for new septic tank installations. While it has the lowest upfront cost, the short lifespan of 15-20 years and safety concerns from lid corrosion make other materials a better long-term investment. Many states have banned or discouraged new steel tank installations.