Concrete
A rigid, heavy shell. Check walls, joints, covers and lifting access.
Septic Tank Installation & Replacement in Olympia, WA
Installation and replacement start with the parcel. A licensed designer or engineer reviews wastewater demand, soils and the disposal area.
Current WA minimum tank storage is 1,000 gallons for up to four bedrooms, plus 250 gallons per added bedroom. Gravity, pressure, mound and treatment designs depend on site approval.
Olympia Tank Sizes and Materials
Start with the actual tank record. Current WA minimum single-family capacities are:
| Bedrooms | Tank minimum |
|---|---|
| 1–4 | 1,000 gallons |
| 5 | 1,250 gallons |
| 6 | 1,500 gallons |
These are code minimums, not an installed-tank average. Final design, treatment and field requirements depend on the property.
Fiberglass
A lighter composite shell. Approved support and backfill protect it.
Polyethylene
A lightweight molded tank. Burial and groundwater limits are model-specific.
Check Sewer First
Confirm utility service and connection requirements for the address. A nearby septic home does not establish approval for your parcel.
Evaluate the Site
The designer reviews soils, seasonal groundwater, wells, setbacks and reserve space. Some parcels need wet-season study.
Match Bedrooms and Capacity
The current state tank minimum is 1,000 gallons for up to four bedrooms; five bedrooms is 1,250 gallons and six is 1,500. The approved design can be larger.
Choose the Treatment Approach
Gravity uses suitable native soil; pressure distribution doses the field. Mounds, sand filters and registered treatment products address different design needs.
Confirm Materials and Access
Use an approved tank model. Concrete needs lifting access; fiberglass and polyethylene need model-specific support, backfill and groundwater precautions.
Complete the Approvals
Submit the required County applications and design. Meet approval conditions before work; arrange final inspection and an accepted record drawing.
Septic Tank Installation & Replacement FAQs
Practical answers for Olympia homes and businesses.
Can every property use gravity septic?
No. Soil, groundwater, slopes, setbacks and approved use determine the design.
Can I install the system myself?
Thurston County does not allow homeowner design or installation, including tank placement. Use the appropriate certified professional.
A Clear Plan for Your Septic System.
Tell us where you are, what is happening and the service you need.