Can a blocked drain cause a leak under the sink?

Yes, and it is a common way a blockage first shows itself. When the line downstream is blocked, water backs up inside the pipe and pushes out at the first joint it reaches. The connection is not necessarily faulty. Tightening it will not hold, because the cause is further down.

Why does a hairdresser's sink block more than a normal one?

Because hair does not break down and a salon sends a lot of it down one pipe. A few strands catch on a rough spot inside the line, then soap, conditioner and product bind more hair to them. The mat grows until the pipe closes, which is why it recurs.

Can drain cleaner clear a hair blockage?

Rarely, once the blockage is established further down the line. The liquid tends to slip past through whatever gap is left rather than working through the mat. It also leaves caustic residue in the pipe for whoever opens the trap next, and repeated use is hard on older pipework.

How do plumbers get hair out of a drain pipe?

With a drain machine. A rotating cable is fed along the line and cuts the mat out, restoring the full width of the pipe rather than punching a channel through the middle of the blockage. That distinction is what decides whether the sink stays clear or blocks again.

Do sink strainers actually make a difference?

Yes, and they are the cheapest fix available. A strainer over every plughole catches hair before it reaches the pipe, which removes the anchor that everything else builds on. In our experience the salons that empty their strainers daily call about blockages far less often.

My salon basin is slow but not blocked. Is that worth calling about?

It is the best time to call. A slow basin means the line is narrowing but still open, so clearing it is straightforward. Waiting until it closes completely usually means the call happens on a trading day, which is the expensive version of the same job.

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Case study · 5 min read

Blocked drain Maroubra: salon sink

A Maroubra salon called Norton Plumbing about a leak under the basin. The cause was a blocked drain. Why hair blockages show up as leaks.

Adam Norton · 17 August 2026

Adam Norton from Norton Plumbing kneeling beside an open under sink cabinet at a Maroubra hairdressing salon, holding a large mass of matted hair cleared from the blocked drain

Norton Plumbing was called to a hairdressing salon in Maroubra where water was leaking from underneath one of the basins. The owner had had her washing basin chair installed by us when she was setting the salon up, so she called back when the leak appeared.

She called it a leak, and she was right about what she could see. But the leak was the symptom. The cause was a blocked drain, and until the blockage came out the water was always going to find its way out somewhere.

Why a blocked drain shows up as a leak

A leak at a basin connection is usually the seal or a loose joint, and that is where any plumber starts. On this one the joint was sound.

That is worth paying attention to, because it changes the diagnosis. Water under a basin has to come from somewhere. If the connection itself is not failing, then the water is not escaping because the joint is weak, it is escaping because it cannot go the way it is supposed to go. A blocked line downstream backs the water up, the level rises inside the pipe, and it pushes out at the first join it reaches. Tighten that join and the water simply finds the next one.

This is the version of a blocked drain that catches people out. Most people are watching for a slow sink. A salon basin that has been draining a little worse each month is easy not to notice when it is being used all day by different people, and the first anyone knows about it is a puddle in the cabinet.

Why hair blocks a salon drain

Hair is the worst thing that goes down a waste pipe, and it is the one thing a salon cannot avoid sending down there.

It does not break down. Fat sets hard and can at least be cut out cleanly. Food scraps eventually soften. Hair just stays, and it behaves like a net. A few strands catch on a rough spot inside the pipe, a joint, a scale patch, an old repair. Once that first anchor is there, every wash after it adds more. Soap, conditioner, colour residue and product bind the strands together until what is sitting in the pipe is a solid rope rather than loose hair.

That is why salons, barber shops and dog groomers get this blockage more than anyone, and why it comes back if only a channel is punched through the middle of it.

A gloved hand holding a large rope of matted hair pulled from a blocked drain at a Maroubra hairdressing salon, with a drain machine on the floor below — What came back out of the line. Hair bound together with soap and product, matted into a single rope. This had been lying across the pipe catching everything that went down after it.

What we found in the line

The first check is always the trap, the curved section of pipe inside the cabinet. It catches a lot of problems and it is the easy fix when the blockage is sitting there.

On this one the trap was clear. That told us straight away the build up was further along the line, out past the cabinet and well beyond the reach of a bucket, a plunger or anything poured down the plughole.

So the drain machine went in. The rotating cable works its way along the pipe and cuts the blockage out rather than pushing a hole through it, which matters more with hair than with anything else. Punch a channel through a hair blockage and the water will run for a fortnight, then the remaining mat catches the next wash and you are back where you started. Take the mat out and the pipe is a full circle again. With the line clear, the water had somewhere to go and the leak under the basin stopped.

Adam Norton from Norton Plumbing working at an open under sink cabinet at a Maroubra salon with a drain machine set up to clear the blocked drain — Cabinet open, trap checked, machine set up. The blockage was past the trap, which is where most salon sink blockages sit.

Why drain cleaner will not shift a hair blockage

This is the one worth being blunt about, because most salons have tried it before they call.

Caustic drain cleaner is sold as a solution for hair, and against a few loose strands in a plughole it does something. Against an established mat sitting further down the line it does very little. The liquid slips past through whatever gap is left rather than working through the blockage, and what it leaves behind is caustic residue sitting in the pipe for whoever opens that trap next. Repeated use is also hard on older pipework.

Boiling water has the same problem for a different reason. It moves the surface of the blockage around. It does not remove it.

Once a line is properly blocked with hair, mechanical clearing is what works.

Blocked drains in Maroubra shopfronts

Maroubra's shopping strips along Maroubra Road and Anzac Parade are largely mid century brick and post war shopfronts, and a lot of the tenancies inside them have been fitted out and refitted several times over. The waste lines under those shops are frequently older than the business currently using them.

That matters because a salon fit out usually inherits the drainage rather than replacing it. A pipe that ran fine as a storeroom sink for twenty years is suddenly taking hair and product ten hours a day. Add the joins, bends and patched sections that come with a pipe that has been reworked a few times, and there are plenty of places for the first strands to catch.

A blocked drain in Maroubra commercial premises is usually this story, not a sudden failure.

How to stop a salon sink blocking again

Sydney Water's Save Our Sinks guidance is aimed at households, but the principle is exactly the same behind a basin that takes hair all day.

A strainer over every plughole, and someone whose job it is to empty them. This is the single highest value thing a salon can do, and it costs almost nothing.
Sweep before you wash. Cut hair that goes into the bin cannot go into the pipe. Most of what blocks a salon line arrives as rinse water, not as a handful of hair down the drain.
Only water, detergent and soap down the sink. Colour residue and product build on top of whatever hair is already in there.
Treat a slow basin as the warning it is, and treat water appearing under the cabinet as the same warning arriving later. Both mean the line is narrowing.
Get the line machined out on a schedule rather than waiting for it to close. For a busy salon this is maintenance, in the same way the coffee machine gets serviced.

How to reach Norton Plumbing

Norton Plumbing has cleared blocked drains for homes and businesses across the Eastern Suburbs since 2019. Adam Norton holds NSW plumbing licence 397768C and is the primary technician on the tools, and the team is based in Coogee. If a sink at your salon, shop or home is slow, gurgling, leaking underneath or fully blocked, see our blocked drains service or our Maroubra plumber page, or call 0477 858 951.

Frequently asked

Common questions

Can a blocked drain cause a leak under the sink?: Yes, and it is a common way a blockage first shows itself. When the line downstream is blocked, water backs up inside the pipe and pushes out at the first joint it reaches. The connection is not necessarily faulty. Tightening it will not hold, because the cause is further down.
Why does a hairdresser's sink block more than a normal one?: Because hair does not break down and a salon sends a lot of it down one pipe. A few strands catch on a rough spot inside the line, then soap, conditioner and product bind more hair to them. The mat grows until the pipe closes, which is why it recurs.
Can drain cleaner clear a hair blockage?: Rarely, once the blockage is established further down the line. The liquid tends to slip past through whatever gap is left rather than working through the mat. It also leaves caustic residue in the pipe for whoever opens the trap next, and repeated use is hard on older pipework.
How do plumbers get hair out of a drain pipe?: With a drain machine. A rotating cable is fed along the line and cuts the mat out, restoring the full width of the pipe rather than punching a channel through the middle of the blockage. That distinction is what decides whether the sink stays clear or blocks again.
Do sink strainers actually make a difference?: Yes, and they are the cheapest fix available. A strainer over every plughole catches hair before it reaches the pipe, which removes the anchor that everything else builds on. In our experience the salons that empty their strainers daily call about blockages far less often.
My salon basin is slow but not blocked. Is that worth calling about?: It is the best time to call. A slow basin means the line is narrowing but still open, so clearing it is straightforward. Waiting until it closes completely usually means the call happens on a trading day, which is the expensive version of the same job.

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