Common Causes of Blocked Drains

It is a sound no homeowner wants to hear—the gurgle of a sink that refuses to drain, or worse, the silence of a toilet that is dangerously close to overflowing. Blocked drains are one of the most frequent plumbing issues faced by Australian households. They can strike at any time, turning a relaxing weekend into a stressful scramble for solutions. While some blockages are sudden accidents, most are the result of a slow accumulation of materials that simply should not be in the pipes.

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Understanding what causes these blockages is the first step toward prevention. Our drainage systems are designed to carry away wastewater and human waste—nothing else. Yet, inadvertently, we treat them like garbage disposal units. From the kitchen sink to the bathroom shower, everyday habits contribute to the narrowing of pipes until, eventually, the water has nowhere to go.

By identifying the main culprits, you can change how you manage waste in your home and potentially save thousands on emergency plumbing repairs.

1. The Kitchen Menace: Grease and Fat

In the kitchen, the number one enemy of clear pipes is cooking oil. It is a common misconception that if you rinse a greasy pan with hot water, the oil will simply wash away. In reality, as that oil travels down the pipe, it cools. When it cools, it solidifies.

Over time, layers of fat, oil, and grease (often referred to as FOG in the industry) coat the inside of the pipes like cholesterol in an artery. This sticky lining traps other food particles—coffee grounds, eggshells, and rice—creating a stubborn, dense blockage known as a "fatberg."

In Australia, particularly during colder months, this happens rapidly. The best practice is to wipe greasy pans with a paper towel before washing them, and pour excess oil into a container to be thrown in the bin, never down the sink.

2. The Bathroom Culprit: Hair and Soap Scum

In the bathroom, hair is the primary cause of slow-draining showers and vanity basins. Human hair is tough and does not break down. When it falls into the drain, it snags on the rough edges of the pipes or catches on the crossbars of the waste outlet.

Once a few strands get caught, they act as a net. They catch more hair, as well as the soapy residue from your shampoo and body wash. Soap scum is surprisingly sticky. Together, hair and soap form a tangled, slimy mass that restricts water flow.

This issue is exacerbated by pet washing. Washing a dog in the bathtub releases a huge amount of fur into the system. Installing a simple mesh drain guard is an inexpensive way to catch this debris before it enters the plumbing.

3. The "Flushable" Myth: Wet Wipes

Perhaps the most damaging trend for Australian sewer systems in recent years is the use of wet wipes. Many brands label their products as "flushable," leading consumers to believe they are safe for the toilet. Plumbers and water authorities will tell you otherwise.

Unlike toilet paper, which is designed to disintegrate in water almost immediately, wet wipes are made with synthetic fibres that hold their shape. They do not break down. When flushed, they can snag on pipe imperfections or tree roots. They clump together with other non-flushable items, causing massive blockages deep in the sewer line.

The rule is simple: only the "Three Ps" (Pee, Poo, and Paper) should ever be flushed. Wipes, sanitary products, cotton buds, and dental floss belong in the bin.

4. The Silent Invader: Tree Roots

In Australia, we love our gardens, but our native trees can be aggressive. Species like Eucalypts, Bottlebrushes, and figs have extensive root systems that are constantly seeking moisture and nutrients. Your sewer pipes contain exactly what they are looking for: water and fertilizer.

Even the smallest hairline crack or a loose joint in an older clay or earthenware pipe releases moisture into the soil. Tree roots detect this and grow towards the source. They are powerful enough to force their way into the pipe. Once inside, they grow rapidly, forming a thick, fibrous root ball that fills the entire diameter of the pipe.

Root intrusion is responsible for some of the most severe blocked drains. These blockages cannot be cleared with a plunger or chemicals; they require heavy-duty equipment like an electric eel or a high-pressure water jetter to cut the roots away.

5. Foreign Objects and Toys

Families with young children are familiar with the mystery of the missing toy. Often, that toy has gone for a swim. Small children are fascinated by the toilet flush, and it is not uncommon for toy cars, action figures, or even toothbrushes to be flushed down the bend.

These solid objects can become lodged in the U-bend (the trap) of the toilet. They might allow water to pass slowly but will block solids, leading to frequent backups. Similarly, toilet deodorizers that hang on the rim of the bowl can sometimes detach and fall in without being noticed, causing a hard obstruction.

6. Incorrect Pipe Installation

Sometimes, the blockage is not caused by what you put down the drain, but by the drain itself. If the plumbing was not installed correctly in the first place, or if the ground has shifted over time, the pipes may not have the correct "fall" or gradient.

Pipes rely on gravity to move waste. If a section of pipe is flat or, worse, has a backfall (slopes the wrong way), water and waste will pool in that section instead of flowing away. This stagnant area allows solids to settle and build up, leading to repetitive blockages. Diagnosing this issue usually requires a CCTV camera inspection to view the pipe alignment underground.

7. Natural Debris: Leaves and Dirt

It is not just internal pipes that get blocked. Your stormwater drains—the ones that carry rainwater from your roof gutters—are also prone to clogging.

In autumn, or after a heavy storm, gutters fill with leaves, twigs, and dirt. If downpipes are not protected with guards, this debris washes down into the stormwater lines. Unlike sewer pipes, stormwater pipes are often smaller and can block easily. A blocked stormwater drain can lead to overflowing gutters and, in severe cases, flooding around the foundation of your home. Regular gutter cleaning is the best defense against this type of blockage.

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Questions and Answers: Common Questions About blocked drains in Australia

Q: Can I use boiling water to clear a blocked drain?

A: You need to be careful. While hot water is great for melting grease in the kitchen sink, pouring boiling water directly into a porcelain toilet bowl can crack it. Also, many modern homes in Australia use PVC (plastic) pipes. Extremely hot boiling water can sometimes soften or warp the PVC joints if used excessively. Very hot tap water mixed with dish soap is safer and often just as effective for grease.

Q: How do I know if the blockage is in my house or the council main?

A: If only one fixture is blocked (like the kitchen sink), the issue is in your house. If multiple fixtures are backing up simultaneously (e.g., you flush the toilet and water comes up in the shower), or if your Overflow Relief Gully (ORG) outside is overflowing, you have a main sewer blockage. In Australia, the homeowner is responsible for the pipes up to the connection point with the council main. If the blockage is in the council's infrastructure (the street), it is their responsibility. A plumber can determine the location.

Q: Are chemical drain cleaners safe to use?

A: Most professional plumbers advise against them. Chemical cleaners rely on caustic acid to burn through clogs. This creates intense heat that can damage plastic pipes and corrode older metal pipes. Furthermore, if the chemical doesn't work, it sits in the pipe. When a plumber arrives to fix it, they are at risk of chemical burns when they cut the pipe. Mechanical methods (plunging or jetting) are safer for your plumbing system.

Q: What is the Overflow Relief Gully (ORG)?

A: The ORG is a small drain grate usually located outside your home, near the kitchen or laundry. It is a vital safety feature. It is designed to be lower than the lowest drain inside your house (usually the shower). If the main sewer line blocks, the sewage will overflow out of the ORG into the garden rather than flooding inside your home. It is crucial to ensure your ORG is not covered by pot plants, paving, or garden mulch so it can function correctly.

Q: Can baking soda and vinegar really clear a drain?

A: Yes, for minor organic blockages, it can be effective. The reaction between the baking soda and vinegar creates fizzing and pressure that helps dislodge grime. It is a great maintenance habit to keep pipes clean. However, for solid obstructions like tree roots or plastic toys, this method will not work.

Conclusion: Your Path to a Successful blocked drains in Australia

Dealing with drainage issues is an inevitable part of maintaining a home, but many blockages are entirely preventable. By being mindful of what goes down your sink and toilet, you can avoid the mess and expense of a backup.

Treat your drains with respect. Keep the grease in the bin, install hair catchers in the shower, and protect your stormwater lines from leaves. Understanding the common causes empowers you to spot bad habits before they turn into plumbing emergencies.