Sunday night in Fairfield, after a family lunch that ran to twenty people. The dishwasher finishes its cycle, pumps out, and the kitchen sink fills with grey water and a slick of oil on top. By the time I get the call on Monday the water has gone down a little, which everyone takes as a good sign. It isn't. The fat has set again with a pinhole through it.
A blocked kitchen sink is one of the most common jobs I do as a plumber across South West Sydney, and one of the few you can usually fix yourself in twenty minutes with a bucket and a plunger. Here's how, why it keeps coming back in some houses, and the signs that tell you it's not the sink at all but the main drain. If you would rather hand it to a licensed blocked drains plumber, no call-out fee, ring 0455 222 292 and Paul answers.
Most blocked kitchen sinks are cooking fat and food scraps set hard in the trap under the sink. Plunge with the second bowl blocked, then put a bucket under the trap, unscrew it, tip it out and refit. Skip the caustic. If the sink keeps blocking, grease has coated the branch pipe and it needs jet blasting. If other drains are slow too, or the gully outside is full, it's the main drain and that's a plumber job.
Why a kitchen sink blocks
Fat. Cooking oil goes down the sink as a liquid, hits the cold trap and the cold pipe past it, and sets. Every wash adds a layer. Rice, pasta, coffee grounds and the scrapings off the plates stick to it, and within a few months the 50 mm pipe under the sink has a 20 mm hole through the middle. Hot water and detergent carry the fat a little further before it sets, which is why the blockage is often just past the trap rather than in it. Sydney Water's advice is only water, detergent and soap down the sink, and they clear up to 20,000 blockages a year in their own pipes. Wipe the pan with paper towel, pour the oil into a jar and bin it. That's the whole prevention plan.
How to clear a blocked kitchen sink yourself
You need a bucket, a plunger, gloves and an old towel.
- Bail the sink down to a few centimetres of water. A plunger needs water to seal, not a full sink to fight.
- On a double bowl, stuff a wet rag into the second plug hole and hold it down. Plunge the blocked bowl firmly a dozen times. If the water drops, run hot tap water for a minute to carry the fat through.
- No luck? Open the cupboard and find the trap: a bottle trap (a cylinder with a screw-off base) or a P-trap (a U-shaped bend with two big plastic nuts). Bucket under it, unscrew by hand, let it drain, lift it away and tip out what's inside. It'll be grey, greasy and it'll smell.
- Rinse the trap in the laundry tub or outside, not in the bathroom basin. Check the washers are seated, refit hand tight, then run the tap and watch for drips.
- Still slow? The blockage is past the trap in the branch pipe. Feed a plastic drain snake through the trap outlet as far as it goes, twist, pull back, refit and test.
If the trap and the snake haven't fixed it, stop there. The fat has coated the branch pipe further along than you can reach, and that's a jet blasting job. Please don't reach for the caustic. I've written up what drain unblockers actually do; the short version is they float on top of a blocked sink, cook the trap and wait for whoever opens it next.
How to clear a kitchen sink trap without flooding the cupboard
Three things people get wrong. They open the trap with the sink still full, and the lot comes out at once. They lose the small rubber washers in the bucket and refit without them. And they tighten the nuts with pliers, which cracks the plastic. Bail first, washers on the bench, hand tight only. If the trap is an old chrome or galvanised one that won't unscrew, or crumbles when you try, leave it: a new trap is a cheap fixture job, and forcing an old one turns a blockage into a leak.
Dishwasher not draining and the sink gurgling: same pipe, same problem
The dishwasher shares the sink's trap. Its drain hose connects to a spigot on the sink waste or on the trap itself, looped up high under the bench so the sink can't siphon back into the machine. When the trap or the branch is half blocked with fat, the dishwasher pump pushes out a lot of water fast, the pipe can't take it, and it comes up in the sink. So a dishwasher not draining properly is usually the sink's problem. Check the machine's filter first, then the trap. The same goes for a sink gurgling as it empties: that's air being dragged through the trap because the pipe past it has narrowed, and it's the early warning, usually weeks before the sink stops. A sink that gurgles when the toilet flushes is a different story, covered below.
On a new kitchen, one more thing. If a dishwasher has never drained properly since the day it went in, the knock-out cap on the spigot may never have been removed. It's a five-minute fix and I see it more than I should. My dishwasher installation guide shows what a proper connection looks like.
Why it keeps happening
Some kitchens block every few months no matter how careful the cook is, and there's usually a reason in the pipework. Long, flat runs of branch pipe with not enough fall let fat settle. Old galvanised branches in the brick homes around Cabramatta are rough inside and half their original diameter with rust. Five adults cooking separately in a rented house puts a restaurant's worth of fat down a domestic line. And a kitchen pipe that drops into a gully outside can have roots in the last metre. A camera through the line tells you which it is, and jet blasting cuts the fat off the pipe wall rather than punching a hole through it, which is why a proper clear lasts years and a plunge lasts weeks. If a renovation is coming, that's the moment to have the kitchen plumbing laid with proper fall and a 50 mm waste.
| Symptom | Likely cause | DIY or plumber? |
|---|---|---|
| Sink slow, greasy smell, dishwasher backs up | Fat in the trap or just past it | DIY: plunge, then clean the trap |
| Blocks again within weeks of clearing | Fat coating the branch, poor fall or old galvanised pipe | Plumber: jet blast and camera |
| Sink gurgles as it empties | Partial blockage past the trap | DIY first, plumber if it continues |
| Sink gurgles when the toilet flushes | Main line partly blocked | Plumber |
| Other drains slow too, gully outside full | Sewer blocked, usually tree roots | Plumber, today |
When it's the main drain, not the sink
A kitchen sink blocked with fat affects the kitchen and nothing else. When the shower is slow at the same time, the toilet burps when the sink empties, or the laundry tub fills when the washing machine drains, the blockage is in the pipe they all share. Go outside and find the overflow relief gully, the grated drain near an outside wall that sits lower than the fixtures inside. If it has water in it or is overflowing, the sewer line is blocked and the gully is doing its job. On the older blocks around Fairfield that's tree roots more often than not, and it needs the jet blaster and the CCTV camera. The blocked drain guide covers what the camera finds and what it costs to fix.
What a blocked kitchen sink costs to fix
If you clear the trap yourself, nothing. If a plumber has to come, the Sydney 2026 price guides put a blocked drain clear at $180 to $450, with a call-out fee of $69 to $170 on top. A camera inspection is quoted on inspection and usually bundled in when the jet blaster is used. What moves the price is access, whether it's fat in the branch or roots in the main, and the time of day. A slow sink can wait until business hours; the rate is the same with us either way, so there is no need to lose sleep over it. A gully overflowing across the yard can't.
Blocked sinks that keep coming back
A kitchen sink that blocks every few months is grease building up in layers along the branch pipe, not one lump in the trap. Plunging clears the trap and leaves the layers. Jet blasting blocked drains scours the pipe walls back to bare pipe, which is why a jetted kitchen line stays clear for years. If the sink and another fixture are slow at the same time, it is the main line, and that is a blocked drains plumber job.
When to call a plumber
Ring me when the plunger and the trap clean haven't cleared it, when the same sink blocks every few months, when the dishwasher keeps backing up into the sink, or when a gurgle has turned into a sink that won't drain at all. Ring straight away if other fixtures are slow or the gully outside is full, because that's the sewer and it won't improve on its own. In NSW, anything beyond cleaning a trap or plunging a drain is licensed plumbing work, and a branch that blocks every few months is telling you about the pipe, not the cook. Done right. Done once.
Monarch Civil & Plumbing clears blocked drains across South West Sydney and the Macarthur region, with the jet blaster and camera on the truck. If you need a plumber in Fairfield or a plumber in Cabramatta, ring 0455 222 292 and you'll get a price before the work starts.
Related guides: do drain unblockers work.
Need it sorted? Ring 0455 222 292 any hour or book online. Monarch Civil & Plumbing is a blocked drains plumber, no call-out fee, across Liverpool, Fairfield, Campbelltown and Camden, and the rate is the same after hours.
Blocked drain in Liverpool, Fairfield or Campbelltown?
The local pages say what is usually wrong in your suburb and what Paul does about it: blocked drains Liverpool, blocked drains Fairfield and blocked drains Campbelltown. Everywhere else within about 20 km of Austral, the blocked drains page covers how a job runs and service areas lists every suburb. No call-out fee anywhere, and the camera goes down before anything is quoted.
Frequently asked
Why is my kitchen sink not draining but not fully blocked?
A slow sink is a partial blockage, nearly always fat that has set in the trap or in the branch pipe just past it, with a narrow channel still open through the middle. It is the best time to act. Plunge with the second bowl blocked, then take the trap off and clean it out. Leave it and the channel closes, usually on a Sunday night with a sink full of dishes.
How do you clear a grease blocked drain for good?
Cleaning the trap deals with the fat you can reach. Fat coating the branch pipe beyond it needs jet blasting, which cuts the build-up off the pipe wall with high pressure water rather than punching a hole through it. A camera afterwards shows whether the pipe is clean and whether poor fall or old galvanised pipe is the reason it keeps setting. Then keep the oil out of the sink.
Can I pour boiling water down a blocked kitchen sink?
Hot tap water, yes, and with a squirt of detergent it helps carry loosened fat through after you have plunged. A kettle of boiling water is a different thing. Modern traps and branch pipes are plastic, and boiling water can soften joints and warp a cheap trap, and it will not melt a set plug of fat in a cold pipe anyway. Never pour hot water into a drain that has had chemicals in it.
Why does my kitchen sink gurgle when the dishwasher runs?
The dishwasher drains through the sink's trap, and its pump pushes water out fast. If the trap or the branch pipe is partly blocked with fat, the water backs up and drags air through the trap, which is the gurgle. Sometimes the sink fills as well. Clean the dishwasher filter, then the trap. If the sink also gurgles when the toilet flushes, the problem is in the main line.
Is it safe to use caustic soda in a kitchen sink?
I would not. In a sink that is already full, caustic soda dilutes and floats on top of the blockage without reaching it, and the heat it produces while reacting sits in the plastic trap and can soften it. It also turns the trap into a burn hazard for whoever opens it next, which is usually the plumber. A bucket, a plunger and ten minutes at the trap does more and costs nothing.
Why does my kitchen sink block every few months?
Something in the pipework is helping the fat settle. Long flat runs without enough fall, old galvanised pipe that is rough and narrowed with rust, a 40 mm waste where 50 mm was needed, or roots in the last metre before the gully outside all do it. A camera inspection after a jet blast shows which one you have. Fixing the cause is usually cheaper than clearing the same pipe twice a year.
Licensed plumber and drainer based in Austral, 13+ years in the trade, working across Liverpool, Fairfield and the Macarthur region. About Paul