Why does my kitchen sink keep blocking?

Because the cause is still in the pipe. Fat build-up narrows the line over years, and a partial clear, hot water or drain cleaner only opens a small channel through it. The remaining build-up catches new fat quickly, so the sink blocks again. A full mechanical clear removes the build-up itself.

Can boiling water unblock a kitchen sink?

Not reliably. Boiling water softens the surface of set fat and moves some of it further down the line, where it cools and hardens again. The sink may drain better for a short while, then slow down again. It can also damage PVC pipes and fittings if poured repeatedly.

Does liquid drain cleaner work on kitchen sink blockages?

Rarely, once a fat blockage is established. The chemical tends to slip past the build-up through whatever gap remains rather than dissolving it. Repeated use is also hard on older pipework, and it leaves caustic residue in the trap for whoever works on the pipe next.

What is the difference between a blocked trap and a blocked line?

The trap is the curved pipe inside the sink cabinet, and it is the easy fix when scraps or fat collect there. A blocked line means the build-up sits further along the pipe, beyond reach of a bucket-and-spanner job, and needs a drain machine or jetter to clear properly.

How do plumbers clear a blocked kitchen sink?

In our experience the usual sequence is trap first, then machine. If the trap is clear, a drain machine runs a rotating cable through the line to cut out the fat and scale build-up, restoring the full pipe width. For long or recurring blockages, water jetting and a CCTV camera inspection can follow.

All articles

Case study · 5 min read

Blocked kitchen sink in Coogee: fixed

A Coogee kitchen sink that would not drain, cleared by Norton Plumbing. Why fat build-up blocks kitchen lines and what actually clears it.

Adam Norton · 23 July 2026

Greg from Norton Plumbing at an open under-sink cabinet in a Coogee kitchen with a drain machine set up to clear a blocked kitchen sink

Norton Plumbing was called to a home in Coogee where the kitchen sink had stopped draining. Greg opened up the under-sink cabinet, checked the trap, then ran the drain machine through the kitchen line until the build-up cleared and the sink drained freely again.

A blocked kitchen sink rarely happens overnight. The line narrows slowly over years, the sink drains a little slower each month, and then one day the water simply stops going anywhere. By the time we are called, the pipe is usually close to fully closed.

What blocks a kitchen sink line

Kitchen blockages are their own category. Bathroom drains block with hair and soap. Kitchen drains block with fat. Cooking fat and oil go down the plughole as warm liquid, then cool inside the pipe and set hard, like candle wax. Each wash adds another thin layer, food scraps stick to it, and over the years the inside of the pipe narrows from a full circle to a gap the width of a pencil.

Hot water from the tap does not undo this. It softens the surface of the fat for a moment and pushes some of it a little further along the line, where it cools and sets again. That is why a slow kitchen sink often seems to improve after a kettle of hot water, then blocks again within weeks.

How Greg cleared it

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 sits there. In this case the trap was clear, which meant the build-up was further along the line, past where any home remedy can reach.

Greg ran a drain machine through the kitchen line. The rotating cable cuts through the fat and scale build-up and restores the full width of the pipe rather than just poking a hole through the middle of the blockage. Then the line gets flushed and the sink gets run to confirm the water is moving properly, not just moving.

Adam and Greg from Norton Plumbing at a Coogee kitchen sink, running the tap to test the drain after clearing the blocked kitchen line — Adam and Greg running the tap after clearing the line, confirming the sink drains freely again.

Why supermarket drain cleaner is not the answer

Caustic drain cleaners rarely clear an established fat blockage. The liquid tends to sit on top of the build-up or slip past through whatever gap remains, and the blockage stays. What it does do is leave caustic chemicals sitting in the pipe, which is unpleasant for whoever opens that trap next, and repeated use is hard on older metal pipework. If a kitchen sink is fully blocked, mechanical clearing is what works.

Kitchen drains in Coogee homes

Coogee has a lot of older homes and unit blocks, and many of their kitchen lines have been collecting build-up for decades. In apartment buildings the kitchen line often runs a long way before it joins the main stack, and in older houses the pipework may have rough internal surfaces that give fat more to grip. A blocked kitchen sink in an older Coogee kitchen is one of the most common calls we get, and it is almost never caused by the last thing that went down the sink. It is the years underneath.

How to keep a kitchen sink draining

Sydney Water spends up to $27 million a year clearing as many as 20,000 blockages from the wastewater network, and its Save Our Sinks campaign gives the same advice we give customers at the door:

Pour fats and oils into a container, let them set, and put the container in the bin. Never down the sink.
Dry-wipe pans and plates with paper towel before washing. Most of the fat that blocks a kitchen line arrives as rinse water from greasy dishes.
Use a sink strainer so food scraps go to the bin or compost instead of the pipe.
Only water, detergent and soap down the sink. Everything else builds up.
Take a slow drain seriously. A kitchen sink that drains slower than it used to is a line that is narrowing. Clearing it at that stage is a smaller job than clearing it after a full blockage.

How to reach Norton Plumbing

Norton Plumbing has cleared blocked kitchen sinks and drains across the Eastern Suburbs since 2019. Adam Norton holds NSW plumbing licence 397768C, and the team is based right here in Coogee. If your kitchen sink is slow, gurgling or blocked, see our blocked drains service or our Coogee plumber page, or call 0477 858 951.

Frequently asked

Common questions

Why does my kitchen sink keep blocking?: Because the cause is still in the pipe. Fat build-up narrows the line over years, and a partial clear, hot water or drain cleaner only opens a small channel through it. The remaining build-up catches new fat quickly, so the sink blocks again. A full mechanical clear removes the build-up itself.
Can boiling water unblock a kitchen sink?: Not reliably. Boiling water softens the surface of set fat and moves some of it further down the line, where it cools and hardens again. The sink may drain better for a short while, then slow down again. It can also damage PVC pipes and fittings if poured repeatedly.
Does liquid drain cleaner work on kitchen sink blockages?: Rarely, once a fat blockage is established. The chemical tends to slip past the build-up through whatever gap remains rather than dissolving it. Repeated use is also hard on older pipework, and it leaves caustic residue in the trap for whoever works on the pipe next.
What is the difference between a blocked trap and a blocked line?: The trap is the curved pipe inside the sink cabinet, and it is the easy fix when scraps or fat collect there. A blocked line means the build-up sits further along the pipe, beyond reach of a bucket-and-spanner job, and needs a drain machine or jetter to clear properly.
How do plumbers clear a blocked kitchen sink?: In our experience the usual sequence is trap first, then machine. If the trap is clear, a drain machine runs a rotating cable through the line to cut out the fat and scale build-up, restoring the full pipe width. For long or recurring blockages, water jetting and a CCTV camera inspection can follow.

Related service