Septic Tank vs AWTS: What's the Difference?

Plenty of homeowners aren't completely sure which system sits in their backyard — and that's understandable, because both live underground and quietly do their job. Here's a plain-English breakdown of how they differ and how to tell them apart.

How a traditional septic tank works

A conventional septic system is beautifully simple. Wastewater from the house flows into a sealed tank where it separates into three layers: solids sink to the bottom as sludge, fats and oils float to the top as scum, and the relatively clear liquid in the middle flows out to a drain field (also called a trench or absorption area) where the soil filters it naturally.

There's no power and no moving parts. The system relies on gravity and the natural bacteria inside the tank to break down waste. That simplicity is its strength — but it also means solids steadily build up and must be pumped out periodically.

How an AWTS works

An Aerated Wastewater Treatment System (AWTS) takes the same waste but treats it to a much higher standard. It uses multiple chambers and, crucially, an air pump that injects oxygen into the wastewater. That oxygen feeds aerobic bacteria, which break down waste far more thoroughly than a standard septic tank.

The treated water is usually disinfected and clean enough to be reused through irrigation on the garden. Because an AWTS has electrical and mechanical parts — pumps, blowers, and alarms — it does more work, but it also needs regular professional servicing to keep running properly.

How to tell which one you have

A few clues make it easy to spot the difference:

• Power supply. An AWTS is connected to mains power and often has a small control box or alarm. A traditional septic tank uses no electricity at all.
• A low humming sound. The air blower on an AWTS runs continuously, so you'll often hear a faint hum near the unit.
• Irrigation in the garden. If treated water is pumped out to sprinklers or drip lines on your lawn, you almost certainly have an AWTS.
• Number of lids. Septic tanks typically have one or two access lids. AWTS units usually have several chambers grouped together.

What each system needs from you

A septic tank mainly needs periodic pumping — typically every three to five years — plus sensible habits about what goes down the drain. An AWTS needs that occasional pump-out too, but it also requires routine servicing of its mechanical parts and, in many council areas, scheduled maintenance to stay compliant.

Whichever you have, the worst thing you can do is ignore it until there's a problem. We service both system types across Sydney, so if you're unsure what yours needs, a quick phone call will sort it out.