Blocked drains: what to check first

The first look

Sydney Water’s signs of a blockage come down to three things you can notice without lifting a lid:

• Water that drains slowly. A sink, the bath or the toilet takes longer than usual to empty.
• Noise. A gurgle from the toilet or from a floor drain.
• Water where it shouldn’t be. A toilet that doesn’t flush properly or has overflowed, or wastewater coming up out of a drain outside the house.

A blockage that goes on long enough doesn’t stay in the pipe: Sydney Water says wastewater can back up and overflow into homes, yards and local waterways.

What usually causes it?

Sydney Water’s list of causes: things flushed that shouldn’t be, fats, oils and grease tipped down sinks, tree roots, and heavy rain overloading the network with stormwater. Non-flushable wet wipes contribute to 75% of wastewater blockages, by its count. Paper towels, tissues, hair and cotton buds don’t break down the way toilet paper does.

What should go down at all?

For the toilet, Sydney Water’s rule is the three Ps:

• Pee
• Poo
• Paper

The paper is toilet paper, plus any product that meets the Flushable Products Standard, AS/NZS 5328:2022. For sinks and drains, only water, detergent and soap. Fats, oils and grease cool and harden in the pipes; Sydney Water suggests sealing oily leftovers in a container for the bin, and a strainer in the kitchen sink.

Is the overflow safe to clean up myself?

Sydney Water says to report it on its faults line, 13 20 90, 24/7. Wastewater contains harmful bacteria, viruses and protozoa that can cause illnesses such as gastroenteritis through direct contact with the wastewater or with surfaces it has touched. Sydney Water’s advice is to stay clear of overflows whether they are on your property or in a public place, to keep children and pets away, and to keep away from overflowing maintenance holes.

Whose job is it to clear?

It depends on where the blockage is. The owner is responsible for the wastewater pipes from the property up to where they connect to Sydney Water’s network, and a blockage in those private pipes needs a licensed plumber. Sydney Water is responsible for the pipes that form its network.

If you aren’t sure which side it is on, Sydney Water says to call 13 20 90, 24/7, and it will ask some simple questions to help work out where the blockage is. The same number reports an overflow from its pipes.

Why does the maintenance hole matter?

Maintenance holes may be on or near a property, usually near the boundary, and they let Sydney Water reach its wastewater and stormwater pipes to clear blockages. If its crews can’t get to them, wastewater or stormwater can back up and flow out of grates or openings into the street, the yard, or possibly inside the home.

What happens when Sydney Water attends an overflow?

It follows a process agreed with regulators. In short:

1. A technician comes to confirm the overflow and assess the risk to people and the environment.
2. Containment goes in straight away, with signs and barricades.
3. A choke crew clears the blockage with a high-pressure water jetter.
4. A clean-up crew removes the solids and contained liquids and cleans the area.
5. The site is walked and sampled, and a lab result confirms it is back to its condition before the overflow.

How do I know the area is safe again?

When Sydney Water’s signs and barricades are gone. Its explanation: after the physical clean-up, once the affected surfaces have dried out in the sun, the microorganisms are no longer at dangerous levels.

Can rain alone cause an overflow?

Yes. Sydney Water describes two kinds. A dry weather overflow, or choke, comes from a blockage in the pipe. A wet weather overflow happens when very heavy rain pushes more water into the wastewater system than it can carry, through cracked pipes, faulty joints, the lids of maintenance holes and direct connections of stormwater pipes. Mark 5 explains why stormwater must stay out of the sewer.

Sydney Water’s own pages, wastewater blockages and avoid wastewater overflows, have the full detail.