Septic Tank vs AWTS: Which System Do You Have?

Hastings Septic Co’s quickest way to tell a conventional septic tank from an aerated wastewater treatment system (AWTS) is to check for a powered control panel and yard sprinklers: a plain, unpowered lid means a conventional tank, needing a pump-out roughly every 3-5 years, while a control box and irrigation mean an AWTS, needing servicing roughly every quarter. Knowing which one you own changes the maintenance, the frequency and the cost.

If you’ve just bought an unsewered property, inherited a system from a previous owner, or simply can’t remember what’s out there under the grass, this page sorts it out before you book the wrong service.

What’s actually different between the two systems?

A conventional septic tank is a passive, one- or two-chamber tank. Wastewater flows in, solids settle to the bottom as sludge, fats and oils float as scum, and the clarified liquid in between drains out to underground absorption trenches, where the surrounding soil does the final treatment. Nothing in a conventional tank runs on electricity; it works purely by gravity and settling, until enough sludge has built up that it needs pumping out. Our guide to how a septic system works walks through the whole process in more detail.

An AWTS is a small, powered treatment plant rather than a passive tank. Wastewater moves through a primary settling chamber, then an aeration chamber where a blower feeds oxygen to the bacteria doing the actual treatment, then a clarifier, then a disinfection stage (commonly chlorine tablets, sometimes a UV unit), before the treated and disinfected water is pumped out to a surface irrigation area through sprinklers or drip lines. Because an AWTS actively treats and disinfects the water rather than relying on trench soil alone, it can be approved to discharge to surface irrigation on blocks where trench disposal isn’t practical.

That single design difference (passive settling and underground trenches versus active aerobic treatment and surface irrigation) is what drives everything else on this page: cost, servicing frequency, and what happens when something goes wrong.

How can you tell which one you’ve got? Visible clues

Most owners can identify their system from the yard in under two minutes, without opening anything.

• A plain, round or rectangular lid (or two) with no power connection and no visible sprinklers is almost always a conventional septic tank. The only outward sign of it working is the absorption trench area, usually a strip of ground that might look slightly greener or lusher than the rest of the lawn.
• A control box with a light, a digital display or a buzzer, plus a power cable running to it, is an AWTS. The box is often mounted near the tank and sometimes labelled with the system’s brand on the lid, worth noting down if you ever need to book a service.
• Sprinkler heads or drip lines fanned out across a defined area of lawn, sometimes roped off or signed, point strongly to an AWTS, since that’s where its treated effluent is irrigated.
• A humming or faint mechanical noise near the tank, especially noticeable at night when the yard is quiet, is the blower running continuously. Conventional tanks make no noise at all.
• The contract of sale or the council file, if you’re buying, should identify the system type along with its approval to operate. If it doesn’t, ask the vendor directly and check with Port Macquarie-Hastings Council before settlement.

If you genuinely can’t tell after checking these clues (a few older or hybrid setups aren’t obvious from the surface), a septic inspection or a quick call with your suburb and any details you already have will usually settle it.

What does each system need, and how often?

This is where the practical difference really lands. A conventional tank is maintained with an occasional pump-out; an AWTS is maintained with regular, ongoing servicing plus its own periodic pump-out.

*Figures above are indicative ranges drawn from our septic pump-out cost guide; your actual price depends on tank size, access, system type and condition, and is always confirmed with a proper quote before work starts.

The AWTS servicing interval isn’t arbitrary. It’s tied to the individual system’s NSW Health accreditation and the operating conditions attached to your council approval, and quarterly is the common expectation for many models, though the binding number is whatever your own paperwork says. If you can’t find it, Port Macquarie-Hastings Council can tell you what’s on file for your property.

What happens if you maintain the wrong system, or ignore the right schedule?

Treating an AWTS like a “set and forget” septic tank is the most common and the most expensive mistake we see. Skip the quarterly servicing and a blower or float switch eventually fails; the treatment bacteria can start dying within days of the air supply stopping, and the system stops disinfecting properly, sometimes silently, sometimes with an alarm that’s easy to learn to ignore. If your control panel is flashing or buzzing, our guide to AWTS alarm troubleshooting covers what the common alarm patterns typically mean and how urgently to act on each.

Going the other way, and simply waiting for symptoms on a conventional tank the way an AWTS’s alarm might let you, doesn’t work either: a conventional tank gives no warning light at all. The first sign is usually slow drains or an odour near the tank, by which point it may already be well overdue, so booking a pump-out on the standard 3-5 year interval (rather than waiting to be told) is the only real strategy for that system type.

Both mistakes tend to converge on the same expensive outcome: damage to trenches or the irrigation area that costs far more to fix than the maintenance would ever have cost.

Which system will I have if I’m buying a property in the Hastings?

Both types are common across the LGA, and there’s no reliable rule of thumb by suburb or age alone. Older acreage properties are somewhat more likely to have a conventional tank simply because AWTS units are a newer technology, while some estate developments and smaller subdivided blocks were specifically approved with AWTS units because soil conditions or lot size ruled out trench-based disposal. The only reliable way to know before you exchange is to check the contract, the section 68 approval on file with Port Macquarie-Hastings Council, and, ideally, arrange a pre-purchase inspection that identifies the system and checks its condition properly.

Does the system type matter for council compliance?

Yes. Both conventional tanks and AWTS units generally require council approval to operate, under section 68 of the Local Government Act 1993, and that approval is typically tied to keeping the system properly maintained: pump-outs on schedule for a conventional tank, servicing records for an AWTS. A buyer’s solicitor or a council inspection program can ask for that maintenance history, and “I’m not even sure what type of system this is” is a poor answer to be giving at settlement or during an inspection.

Septic tank vs AWTS FAQs

How do I know if I have a septic tank or an AWTS without digging anything up?

Look for a powered control box with a light or buzzer and sprinklers across a defined patch of lawn: that combination means an AWTS. A plain lid with no power connection and no sprinklers is a conventional septic tank. A faint mechanical hum near the tank, day or night, also points to an AWTS’s blower running continuously.

Can a conventional septic tank be converted to an AWTS, or the other way around?

Converting between system types is a significant alteration that generally needs fresh council approval, since it changes the approved land-application method (underground trenches versus surface irrigation) as well as the equipment itself. It’s a job for licensed plumbers working through the proper council approval process, not a straightforward swap.

Does an AWTS ever need a pump-out like a conventional tank?

Yes. An AWTS still accumulates sludge in its primary chamber and needs periodic desludging, similar to a conventional tank, just on top of its regular quarterly-style servicing rather than instead of it. Sludge levels are usually checked at each scheduled service so the desludge doesn’t come as a surprise.

Which system costs more to maintain over time?

An AWTS generally costs more per year than a conventional tank’s averaged pump-out cost, since it’s serviced roughly quarterly (indicatively $150-$300 per visit) plus a periodic desludge, versus a conventional tank’s single pump-out every 3-5 years (indicatively $350-$550+). The trade-off is active treatment and the ability to irrigate on the surface, which some blocks genuinely need because trench disposal isn’t suitable for their soil.

What if an alarm is going off and I’m not sure it’s an AWTS?

If there’s a control panel with a light or buzzer active, treat it as an AWTS alarm regardless of what else you know about the system, and don’t ignore it: it usually means a pump, blower or float switch has failed. Our AWTS alarm troubleshooting guide explains what different alarm patterns typically mean and how urgently to respond to each.

I still can’t tell which system I have. What now?

Send us your suburb and a description (or a photo) of whatever’s visible in the yard, a lid, a control box, sprinklers, and we can usually confirm the system type before booking anything, so you don’t end up arranging the wrong service. You can also get a free quote and simply mention you’re not sure which system you have; we’ll help work it out first.

Get the right service booked the first time

Knowing which system you’ve got means booking the right job the first time: a pump-out for a conventional tank, or scheduled servicing for an AWTS, instead of paying for the wrong one. Tell us your suburb and what you can see in the yard, and we’ll confirm the system type as part of arranging your quote.