NSW council guidance puts a conventional septic tank clean every 3 to 5 years depending on use, sooner if drains slow, gurgle, smell persistently or back up, and an aerated system also needs a service every three months.

Two NSW councils that publish a desludging interval arrive at the same outer mark. MidCoast Council says a septic treatment tank should be desludged every 3 to 5 years (dependent on usage). Shoalhaven Water says cleanouts are recommended every 5 years.

Put side by side, 5 years is the longest either suggests a conventional tank should go between cleans, and a busy household belongs at the shorter end. That's our reading of the two councils' guidance, not a law, and your own council's conditions come first.

Some signs override the calendar: slow drains, gurgling pipes, a smell that won't go away, or water backing up into the sink. If you have any of these, book a clean now.

How often should a septic tank be cleaned?

Cross-section of a buried conventional septic tank. The house drain enters on the left. Inside are three layers: floating scum on top, clearer liquid in the middle and settled sludge on the bottom. An outlet pipe on the right runs to a gravel absorption trench under the lawn. A year counter runs from 0 to 5 while the sludge layer thickens, and near year 5 small solids drift out the outlet toward the trench. Lawn House drain Scum Liquid Sludge Outlet Absorption trench Year 0 Year 1 Year 2 Year 3 Year 4 Year 5 Cross-section of a buried conventional septic tank. The house drain enters on the left. Inside are three layers: floating scum on top, clearer liquid in the middle and settled sludge on the bottom. An outlet pipe on the right runs to a gravel absorption trench under the lawn. A year counter runs from 0 to 5 while the sludge layer thickens, and near year 5 small solids drift out the outlet toward the trench. Lawn House drain Scum Liquid Sludge Absorption trench Outlet Year 0 Year 1 Year 2 Year 3 Year 4 Year 5

Desludge every 3 to 5 years (dependent on usage)MidCoast Council

Cleanouts recommended every 5 yearsShoalhaven Water

Shoalhaven Water: sludge must be removed "to avoid system failure such as blockages and the transfer of solids to your disposal area".Source: MidCoast Council, Shoalhaven Water

Every 3 to 5 years is the working range, and usage decides where you sit in it. More people in the house, a smaller tank, heavy water use and the wrong things down the drain all fill the bottom of the tank faster. A couple in a large tank who are careful with the sink will go longer than a family of six on the same tank.

Shoalhaven Water allows for the careful end too: if carefully operated, systems can last several years before a cleanout is required.

The reason for the clean is the sludge. Solids settle in the tank over time, and that sludge must be removed in order to avoid system failure. Left too long, it causes blockages and sends solids on to your trench or second collection tank. Once solids reach the trench, the problem is no longer in the tank. If that has happened, our page on absorption trench problems explains what comes next.

MidCoast puts the upside plainly: routine desludging may extend its useable life, meaning the system's.

One caution. Council guidance is a guide, not a single rule for every tank in the state. The conditions on your council's Approval to Operate are what apply to your property, so check them. And if no one in the house knows when the tank was last cleaned, treat it as due.

Septic tank, aerated system or pump-out: which rules apply to yours?

SystemWhat it needsWhat sets the timingWho arranges itSource
Conventional septic tankDesludge every 3 to 5 years (dependent on usage)MidCoast CouncilCleanouts recommended every 5 yearsShoalhaven WaterUsage and your council's conditionsMidCoast CouncilThe owner books a contractorShoalhaven WaterMidCoast Council, Shoalhaven Water
Aerated system (AWTS)Serviced every 3 months by an accredited agent, a NSW Health requirementMidCoast CouncilA cleanout when the agent advisesShoalhaven WaterThe service agentShoalhaven WaterThe owner engages the agentMidCoast CouncilThe agent must be on site at the cleanoutShoalhaven WaterMidCoast Council, Shoalhaven Water
Pump-out holding tankCollection well emptied periodically by an approved liquid waste transporter, so it does not overflowMidCoast CouncilTank capacity and household water useMidCoast CouncilThe owner engages their own contractorLake Macquarie City CouncilMidCoast Council, Lake Macquarie City Council

"Septic" covers three quite different set-ups, and each has its own rhythm.

A conventional septic tank is the one the 3 to 5 year guidance is written for. You book the clean.

An aerated wastewater treatment system (AWTS) runs on a much tighter schedule. Shoalhaven Water says it must be serviced quarterly by a qualified agent. MidCoast sets the same rhythm, every 3 months by an accredited agent, and calls it a NSW Health requirement that the property owner must arrange.

Over a 5 year stretch, that adds up to about 20 service visits for an aerated system, by our estimate of 4 visits a year for 5 years. A conventional tank gets one clean in the same period. The service agent advises when a cleanout is needed, so with an AWTS the timing is their call, not the calendar's. If you have a Flow System unit, our Flow System page has more.

A pump-out (holding tank) system stores everything and treats nothing. MidCoast says an approved liquid waste transporter must empty the collection well periodically so it doesn't overflow. How often depends on the tank's capacity and the household's water use. Lake Macquarie says owners of these systems must engage their own service contractor for regular pump-outs.

Signs your tank needs pumping out

Four signs to act on now

Shoalhaven Water: attend to these immediately.

Shoalhaven Water names four signs:

The council says these should be attended to immediately.

A full tank, or a faint smell now and then, isn't a failure. Shoalhaven Water says septic tanks are meant to be full and some odour is not unusual.

The word that matters in that list is "persistent". A smell that hangs around for days, or a sink that won't clear, is the signal. A whiff on a still evening isn't.

If water is coming back up into the house, our guide to emergency measures for septic system failures covers the first steps. Leave tank work itself to a professional. For a longer list of signs to watch, see Assessing the Health of Your Septic System: Warning Signs.

What happens on pump-out day?

  1. 1 Before The tank lid is found and cleared of grass, plants and weeds, and a cracked lid is noted for repair.Shoalhaven Water
  2. 2 The clean Sludge and solids are pumped out. For an AWTS, the service agent is on site to show where to pump from.Shoalhaven Water
  3. 3 After The tank is refilled proportionately "to avoid the tank from popping out of the ground".Shoalhaven Water

Write down the date

Source: Shoalhaven Water

The day itself is simple, and most of your part happens before the truck arrives.

Then write the date down. Our 7 Questions to Ask Before a Septic Tank Clean covers what to ask before you book.

Habits that stretch the time between cleans

Inside the house

Dungog Shire Council

Around the tank and trench

Dungog Shire Council and Shoalhaven Water

Every clean you put off costs you nothing if the tank is healthy. These habits, from Dungog Shire Council, are what keep it healthy.

Outside, Shoalhaven Water adds that excess rain getting into the tank can cause your system to fail. It also says trenches do best away from trees, in direct sun, with the grass mown. Our posts on heavy rain and septic systems and tree roots go further on both.

Enzyme products and additives aren't a substitute for a pump-out. Shoalhaven Water says they may assist but still recommends a cleanout at least every 5 years. Good habits, by the same page's account, can significantly increase the time between cleanouts. That's a longer gap, not no cleans at all.

Keep the paperwork: approvals, history and a log

Conventional tank

"every 3 to 5 years (dependent on usage)"MidCoast Council

"at least every 5 years"Shoalhaven Water

Aerated system

"every 3 months, by an accredited agent"MidCoast Council

Warning signs

Slow drains, gurgling, persistent smell, backing upShoalhaven Water

Approvals

Two, one to install and one to operate, with council inspectionsNSW Office of Local Government

Source: MidCoast Council, Shoalhaven Water, NSW Office of Local Government

In NSW, the owner answers for the system. The Office of Local Government says owners must hold two council approvals, one to install and one to operate. Councils then carry out regular inspections and may charge fees, and the owner is responsible for the system being approved and working properly.

A dated record of cleans is the simplest way to show a system has been looked after. The NSW Office of Local Government's The Easy Septic Guide includes a maintenance log sheet you can use for exactly that.

If you're buying a property on septic, ask for the pump-out history before you sign. Some councils will help you check: MidCoast Council offers pre-purchase septic inspections at no charge. That's MidCoast's own offer, and other councils vary, so ask yours.

Booking a septic tank clean with Ward Septics

If your tank is at or past 5 years, if nobody can find the date of the last clean, or if one of the four signs has shown up, that's the time to book.

Ward Septics is owner-operated. Paul has worked as a plumber for more than 45 years, and he covers the Central Coast, Lake Macquarie and the Lower Hunter, including Gosford and Wyong. The truck carries 90 metres of hose, so it can reach the tank without driving onto your property, which keeps it off the absorption area.

To book, call Paul on 0438 315 514. Tell him roughly when the tank was last cleaned and where the lid is. You can read more about the service on our Septic Tank Cleaning page, and check your suburb on Septic Pump-Out Locations.

Call and you talk to Paul, not a call centre.

Call 0438 315 514

Sources