Septic vs Sewer: What Southern Highlands Homeowners Need to Know

If you have recently moved to the Southern Highlands from Sydney or another urban area, there is a reasonable chance your new property came with a system you have never had to think about before: a septic tank. And if you grew up on a rural property, you may have a working knowledge of how they operate but be less certain about what the current regulations require.

Either way, understanding the difference between a septic system and a mains sewer connection, and what each means for how you maintain your property, is genuinely useful information for any Southern Highlands homeowner.

The Basic Difference

Properties connected to town sewer send all wastewater, from toilets, sinks, showers, and laundry, into the council-managed sewer network. From there, it travels to a centralised treatment facility. The homeowner’s responsibility ends at the boundary of their property.

Properties on septic systems manage their wastewater on-site. The septic tank receives all wastewater, separates solids from liquid, and allows the liquid effluent to drain into a designated absorption area (often called a leach field or transpiration area) in the yard. The solids remain in the tank until pumped out by a licensed contractor.

Which System Does Your Property Have?

Many properties in the outer areas of Bowral, Moss Vale, Mittagong, and Bargo, and most rural properties in the Southern Highlands, are on on-site sewage management systems. If you are not sure which applies to your property, your council can confirm. Wollondilly Shire Council and Wingecarribee Shire Council both maintain records of on-site sewage management approvals.

What Septic System Owners Are Responsible For

Owning a septic system comes with maintenance responsibilities that sewer-connected properties do not have.

Regular pumping

The tank needs to be pumped out by a licensed contractor on a regular basis, typically every three to five years depending on household size and usage, though this varies. Neglecting this leads to solids overflowing into the absorption area, which is difficult and expensive to remediate.

What you flush matters

Unlike sewer systems where dilution and centralised treatment handle a wide range of inputs, septic systems rely on bacterial processes to break down waste. Flushing wipes (including those labelled “flushable”), feminine hygiene products, chemicals, cooking oils, or large amounts of disinfectants can disrupt or damage the system.

Absorption area care

The leach field should not be driven over, planted with deep-rooted trees, or built upon. Compaction or root intrusion can render the absorption area ineffective.

Council inspections

Some councils require periodic inspections of on-site sewage management systems. It is worth checking what obligations apply to your property.

When To Call a Plumber

A plumber with experience in rural and on-site sewage systems can help with:

• Diagnosing issues such as slow drains, odours, or soggy ground near the absorption area
• Identifying whether the tank needs pumping or whether there is a more significant fault
• Installing or repairing components such as distribution boxes, inspection points, and inlet/outlet baffles
• Advising on system upgrades where an older system no longer meets current standards

If you notice wet patches in your yard that do not dry out, a persistent sewage smell, or drains that are backing up across multiple fixtures, these could indicate that the system needs attention sooner rather than later.

Team Penguin Plumbing works with septic and on-site sewage systems across the Southern Highlands. Call 0432 374 689 to discuss what you are seeing or to arrange an inspection.

Frequently Asked Questions

How do I know if my property is on septic or sewer?

Your council can confirm this. On a property on septic, you will typically find a tank lid somewhere in the yard, often concrete, sometimes plastic, and an absorption area that may look like a gravel-filled trench or mounded area.

Can a plumber pump out my septic tank?

Septic tank pump-out is typically carried out by a licensed liquid waste contractor rather than a plumber. However, a plumber can inspect the inlet and outlet conditions, diagnose related plumbing faults, and advise on the condition of the system overall.

What should I never flush if I am on septic?

Wipes of any kind, cotton products, cooking grease or oils, chemical drain cleaners, large amounts of bleach or disinfectant, and medications. These either do not break down, kill the bacteria the system relies on, or cause physical blockages.

How long do septic systems last?

A well-maintained septic tank can last 20 to 40 years. The absorption area has a shorter lifespan and may need remediation or replacement if it becomes saturated or damaged.

My yard is wet near the absorption area. Is that a problem?

It could be a sign that the absorption area is overloaded, saturated, or failing. This warrants a professional inspection. Do not ignore it, as an overflowing system can present a health risk and may require council notification.

Questions about your septic system? Call 0432 374 689. We work with on-site sewage systems across the Southern Highlands.