The default system: wastewater settles in a buried tank, then flows by gravity out to a trench or bed of gravel and perforated pipe, where soil bacteria finish treating it. No pump, no electricity, no service contract — the cheapest option by a wide margin, but it depends on soil that percolates (drains) well and a water table that stays low enough beneath the field.
Most home sites with soil that drains reasonably well and enough land for a standard field.
| Bedrooms | Estimated installed cost |
|---|---|
| 1–2 bedrooms (750-gal tank) | $3,400 – $6,800 |
| 3 bedrooms (1,000-gal tank) | $4,000 – $8,000 |
| 4 bedrooms (1,250-gal tank) | $4,600 – $9,200 |
| 5+ bedrooms (1,500-gal tank) | $5,400 – $10,800 |
Soil condition and region can move these numbers 25–35% in either direction — use the full calculator for a range tuned to your site.
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