Septic Tank Backing Up? What to Do in the First Hour, Who to Call, and How to Clean Up Safely

If sewage is backing up from your septic system, stop all water use in the house now, check whether the overflow relief gully outside is spilling, keep people and pets away from anything wet, and call for a same-day or next-morning emergency pump-out on 0468 278 123. Do not flush “just once”, do not pour anything down the drain, and do not open the tank. The rest of this guide explains why each of those steps matters, how to tell whether the fault is the house drain, the tank, the trench or a failed pump, which trade fixes each one, and how to clean up without making anyone sick.

The first hour

1. Stop the water. Every litre that goes down a drain now comes back up somewhere. No flushing, no showers, no washing machine or dishwasher, no taps left running. Tell everyone in the house.

2. Find the overflow relief gully. The ORG is the grated drain outside, usually near the bathroom or laundry, set lower than the indoor fixtures. It is designed so that when the line backs up, sewage surfaces there instead of in the house. If it is bubbling or overflowing, the blockage is at or beyond it: the tank or the trench. If the ORG is dry and sewage is coming up inside, the blockage is in the house drains upstream of the ORG.

3. Keep people away. The Easy Septic Guide is direct: septic tanks do not kill pathogenic bacteria, viruses or parasites. Wet floors, damp carpet and puddles at the gully are all contaminated. Keep children and pets out, and keep your own hands away from your face.

4. If it is an AWTS, check the alarm panel and the power. A sounding or flashing alarm means the irrigation pump, the air blower or the water level has tripped. Mute the buzzer (most panels mute for 24 hours, then sound again), cut water use, and check whether the power to the unit has gone off; a power failure stops the pump and every manufacturer says the system will overflow once its emergency storage is used up, which is only around 1,000 litres on the common units. Do not switch the system off “to reset it” unless the service agent tells you to.

5. Call. For a tank or trench backup: an emergency pump-out, same-day or next-morning, at the routine price plus the $150 to $300 emergency modifier. For a blockage inside the house drains: a licensed plumber. If you are not sure which, call us; the ORG check in step 2 usually answers it in a sentence.

Drain, tank, trench or pump: which is it?

A backup has four common causes, and each belongs to a different trade.

The line between “our job” and “a plumber’s job” is set by law, not by us. Under the Plumbing and Drainage Act 2011 the drain from the house to the septic tank inlet is a sanitary drainage system, and clearing, repairing or replacing it is licensed drainage work; NSW Fair Trading puts the penalty for unlicensed plumbing and drainage work at $22,000 for an individual. Pumping out a tank, servicing an AWTS and jetting an existing trench are not licensed plumbing work. So: if the camera or the ORG test shows the problem is upstream of the tank, we tell you and point you to licensed plumbing and drainage contractors we work with, whose NSW licence number appears on the quote. If it is the tank or beyond, we get on with it.

Why it backed up

The causes worth knowing, because most of them are preventable:

• Solids in the tank past the one-third mark. The NSW Office of Local Government’s rule is to desludge once sludge and scum reach one-third of tank depth, roughly every 3 to 5 years at full occupancy. Past that, solids carry over to the trench and the tank stops accepting flow. The frequency guide explains it.
• A collapsed outlet tee or missing effluent filter. The square junction on the outlet keeps scum inside the tank; when it corrodes off, grease and solids seal the trench. A $250 to $650 repair, found only when someone looks inside.
• A saturated trench. The Hunter’s wettest months are February to April. On the Maitland floodplain, the coalfields clay and the low sand around Medowie and Salt Ash, a trench with no spare capacity backs up at the first big rain and recovers in a dry week. A tank carrying too much sludge is usually the extra load that tips it over.
• Wipes, fats and chemicals. “Flushable” wipes, cooking fat and bleach in quantity are the top three items in blocked drains and dead tanks. The Easy Septic Guide’s don’ts are the whole list.
• AWTS power and pumps. Fuji Clean, Taylex and Ozzi Kleen manuals all say never turn the power off; without the irrigation pump, effluent has nowhere to go and the unit overflows once its 1,000-litre-or-so emergency storage is used. Ozzi Kleen documents a common failure where the float cable slips out of its groove, the float never turns the pump off, and the pump runs dry until it dies.
• Floods. After a flood, NSW Health’s advice is to keep the whole system out of use until floodwater has dropped below the disposal area and the system has been inspected by a licensed plumber or an authorised service technician. A flooded tank is not a backup you fix by pumping harder.

What the emergency visit involves

The truck pumps the tank down, which relieves the backup immediately, then the operator looks at the inlet and outlet tees, the baffle and the liquid level to work out what caused it. If the tank was simply over-full, that is the fix and the routine advice applies afterwards. If the outlet tee is gone or the filter is missing, we tell you what the repair costs. If the trench is the problem, the pump-out buys time and we come back in dry weather for trench diagnostics. If a drain camera shows a blockage upstream of the tank, that is the plumber’s call.

Two things we will not do: enter the tank (under the NSW Confined Spaces Code of Practice, putting your head or upper body through the lid is confined-space entry, and the hydrogen sulphide released by disturbed sludge settles at the bottom), or pump a tank in saturated ground without telling you to refill it, because an empty tank in wet soil can float and snap its pipes. The waste is transported and disposed of under NSW EPA waste rules at a licensed treatment facility that has agreed to accept it; Hunter Water’s plants take tanker loads between 7am and 3pm on weekdays, so a Saturday night pump-out is held in the sealed truck until Monday, which changes nothing for you.

Prices: the routine pump-out band for your tank size ($350 to $500 up to 3,000 litres, $400 to $650 for 3,500 to 4,500 litres, $650 to $900 above 5,000 litres) plus the emergency dispatch modifier of $150 to $300. Buried lids and long hose runs are quoted the same way as on any job.

Cleaning up safely inside

If sewage came up indoors:

1. Ventilate: open windows and doors, and keep the room closed off from the rest of the house.
2. Gloves, boots and eye protection before touching anything. Wash hands thoroughly afterwards and before eating; the Easy Septic Guide’s point about pathogens applies to every surface the water touched.
3. Remove standing liquid with a wet vacuum or mop and bucket; dispose of the water down a drain only after the system is working again, or into the pumped tank.
4. Hard surfaces: wash with detergent and hot water, then disinfect with a household disinfectant, then rinse. Carpet, underlay and soft furnishings that soaked through generally cannot be reliably cleaned and are better removed.
5. Anything used for the clean-up (mop heads, cloths) is contaminated; bag and bin it.
6. Do not use the toilets, laundry or kitchen drains until the system has been pumped or repaired. NSW Health’s flood advice applies to any backup: use less water, fewer flushes and shorter showers until the system is confirmed working.

If a large area was affected, a professional flood or biohazard cleaner is a reasonable call, and your insurer may require one.

Is it covered by insurance?

Home insurance policies commonly treat a sudden, accidental escape of liquid differently from a gradual problem such as a tank that has not been pumped in a decade or a trench that failed over years. Whether a backup is covered depends on the policy wording and the cause, so check your product disclosure statement and call your insurer before paying for a clean-up you hope to claim. What helps a claim is a clear cause on the pump-out docket and inspection report, which is one reason we write both up plainly.

Preventing the next one

• Pump on sludge depth, not the calendar; we measure at every visit.
• Fit an effluent filter on the outlet (the OLG guidelines recommend one; the Easy Septic Guide says to have a plumber fit one) and have it rinsed at each pump-out.
• Keep wipes, fats and bulk chemicals out of the drains.
• Keep the AWTS powered, serviced every three months, and the alarm panel somewhere you will hear it.
• Know where your ORG and your tank lid are before you need them at 9pm. If the lid is buried, a riser ($250 to $450) is the difference between a 30-minute emergency and a two-hour one.

Frequently Asked Questions

Is it the drain or the tank?

Look at the overflow relief gully outside. If it is overflowing, the blockage is at or beyond it (tank or trench) and a pump-out is the first move. If the gully is dry and sewage is inside the house, the house drain is blocked and that is licensed plumbing work.

Who do I call first, a plumber or the septic truck?

Whichever the gully test points to. If you cannot tell, call us; we will ask two questions and send the right trade. Clearing the drain between the house and the tank is licensed drainage work in NSW, so we do not do it; pumping the tank and fixing what is inside it is ours.

Can I flush once if I really have to?

No. Every litre goes back up. Use a neighbour’s bathroom or a bucket with a bin liner until the truck has been.

Why does it only back up when it rains?

The trench is saturated and cannot accept more water, so flow backs up the line. That means the trench has no spare capacity; pumping the tank relieves it, and a trench inspection in dry weather tells you whether it is clogging or just overloaded.

How quickly can a truck come?

For a sewage backup, an active high-water alarm or an overflow, same-day or next-morning dispatch, with the $150 to $300 emergency modifier on the routine pump-out price. Call 0468 278 123; the line is answered outside business hours for emergencies.

Is the clean-up dangerous?

Sewage carries bacteria, viruses and parasites that a septic tank does not kill. Gloves, boots, eye protection, ventilation, detergent then disinfectant on hard surfaces, and removal of soaked soft furnishings is the safe minimum. For a large spill, use a professional cleaner.

Sources and further reading

• NSW Office of Local Government, The Easy Septic Guide: health warnings, the don’ts list, effluent filters, safety at open tanks.
• NSW Office of Local Government, Onsite Wastewater Management Guidelines (April 2025): the desludging rule, trench clogging, AWTS fault checklist.
• NSW Health, Flooding and on-site wastewater systems: what to do after a flooded system.
• Plumbing and Drainage Act 2011 (NSW): why the house drain is licensed drainage work.
• NSW Government, Plumbing, draining and gasfitting licences: licence requirements and penalties.
• SafeWork NSW, Confined spaces: hydrogen sulphide and confined-space entry.