Updated October 20, 2026
Short answer
A conventional gravity system is simpler and cheaper and works where soil drains well with room for a standard drainfield. An aerobic treatment unit (ATU) treats wastewater more thoroughly and is required on tighter soils or smaller lots — it costs more but fits where conventional won't.
Conventional gravity systems
Wastewater settles in the tank and flows by gravity into a drainfield, where it filters through the soil. It's the lowest-cost option, ideal where soil percolates well and there's space for a full-size field.
Aerobic treatment systems (ATU)
An ATU aerates and treats wastewater to a clear, odorless effluent — tested to NSF Standard 40 — before dispersing it by spray or drip. It works on smaller lots and tighter, slower-draining soils a conventional field can't handle.
Which one you'll need
Your soil and perc test decide. We run the evaluation and recommend the right system for your land — and handle the permitting either way.
Free tool
Will your lot need an aerobic system? Check the address.
USDA soil rating, FEMA flood zone, and mapped wetlands for any Texas address — plus the system type and flat price you're likely looking at. About ten seconds, no account.
| Conventional gravity | Aerobic (ATU) | |
|---|---|---|
| Best for | Well-draining soil, room for a full field | Tight/clay soils, smaller lots |
| Treatment | Settling + soil filtration | Aerated to clear, odorless effluent (NSF 40) |
| Drainfield | Standard gravity trenches | Spray or subsurface drip |
| Upfront cost | Lower | Higher |
| Maintenance | Minimal | Periodic (aerator + service) |
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