Updated June 15, 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.
| 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) |
Quick Flow Septic installs new septic systems across Harris County · Montgomery County · Fort Bend County · Waller County · Liberty County.
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