Why does my kitchen sink keep blocking?

Most often grease and food scraps building up in the trap or waste pipe. Water Corporation says fats, oils and grease cause about 30% of wastewater blockages. Wipe pans, bin leftover oil, and use a sink strainer. If it keeps happening after a clear, the plug may be further down the line.

Can I tip boiling water or chemicals down a blocked sink?

Boiling water alone rarely clears a real grease plug and can crack porcelain. Caustic or acid drain cleaners are worse: they sit in the pipe, can burn skin if the sink backs up, and make the plumber’s job unsafe. Bail, plunge, or call us.

My sink and dishwasher are both backed up. Is that one job?

Usually yes — they often share the same waste. Clear or call before running another dishwasher cycle, or you’ll flood the sink.

The bathroom is slow as well. Is that still a sink problem?

No. If more than one area of the house is slow, or the outdoor overflow relief gully is full, the blockage is further down the property sewer. Stop using water and call (08) 6187 3999 or text 0406 882 648. Call Water Corporation on 13 13 75 as well if sewage is overflowing.

Do you clear blocked bathroom vanities and laundry troughs too?

Yes. Hair and soap in a vanity, or lint in a laundry trough, are the same kind of local waste-pipe job. Tell us which room when you book.

Perth · Blocked sinks and drains

Blocked kitchen sink in Perth? What to do (and when to call)

A kitchen sink that won’t drain is usually grease cooled hard in the trap or the waste pipe, food scraps that got past the strainer, or a dishwasher hose sharing the same choke. The fix is different if the bathroom and laundry are slow too — that means the problem is further down the property drain, not just under the sink.

The short answer

If only the kitchen sink (and maybe the dishwasher) is slow, clear what you can from the grate, try a sink plunger on a sealed plug hole, and don’t tip caustic drain chemicals in. Water Corporation says fats, oils and grease hardening in pipes cause about 30% of its wastewater blockages, and asks you to wipe greasy dishes and bin leftover oil instead of washing it down. If the sink won’t clear, or other fixtures are slow as well, call McDermott Plumbing on (08) 6187 3999 or text 0406 882 648. If sewage is overflowing on the property, also call Water Corporation on 13 13 75.

Is it just the sink, or the whole house?

Run the bathroom basin, the shower and a toilet. If those still drain normally, the choke is almost certainly in the kitchen trap, the short waste pipe under the sink, or the dishwasher connection on that line. If several fixtures are slow, a toilet gurgles when the sink empties, or the outdoor overflow relief gully is full, stop using water and treat it as a property-drain blockage — see our blocked toilet and overflow relief gully pages.

Grease, fat and what not to tip in

Water Corporation’s “what not to flush” guidance is blunt: fats, oils and grease that harden in pipes cause about 30% of wastewater blockages. It asks you to pour leftover cooking oil into a container and put it in the bin, wipe greasy pots with paper towel before you wash them, and keep a strainer in the sink so scraps don’t go down. Milk, coffee grounds and tea leaves are on the same list because the fat and solids build up in the pipe.

Caustic drain openers and “acid” cleaners rarely shift a real grease plug, can damage fittings, and make the job unsafe for whoever opens the trap. Skip them.

What to try before you call

Bail standing water into a bucket so you can see the grate. Scoop out food scraps and wipe grease off the grate.
If you have a dishwasher on the same waste, turn it off and don’t run another cycle until the sink clears.
Try a cup-style sink plunger over the plug hole with enough water to cover the cup. Several firm plunges often move a soft plug in the trap.
If you are comfortable with basic tools, place a bucket under the U-bend, undo the slip nuts, and clear the trap. Put it back firmly so it doesn’t drip.
Don’t put your hand into water that might have chemicals in it, and don’t keep running the tap to “push it through” — that overflows the sink or pushes the plug further down.
If it still won’t go, or it clears and blocks again within days, call (08) 6187 3999 or text 0406 882 648 with your suburb and whether any other fixtures are slow.

Dishwashers, waste disposers and shared stacks

Dishwasher: many kitchens tee the dishwasher hose into the sink waste. A grease plug there backs water into both. We clear the shared section and check the hose isn’t kinked or full of sludge.
Waste disposer: it’s meant for soft scraps, not fat, bones or fibrous peelings. A jammed or overloaded disposer can look like a blocked sink; we’ll tell you which it is.
Strata apartments: if your sink and your neighbour’s both slow down, the shared stack may be the problem. Tell the building manager, and we’ll be clear about what is your lot and what is strata.
Commercial kitchens and cafés: we clear kitchen-line and floor-waste blockages. Pumping a grease trap is a liquid-waste contractor’s job, not ours.

What we do

We find whether the blockage is in the trap, the kitchen branch, or further down the property drain, then clear it from the right access point — often under the sink, sometimes from a gully or inspection shaft. For heavy grease or sand further down the line we may use the hydro jetter. If it’s a repeat blockage, a drain camera can show whether grease, a foreign object or a damaged section is the cause. You’ll get a straight answer on what we found and what will stop it coming back.

Common questions

Why does my kitchen sink keep blocking?: Most often grease and food scraps building up in the trap or waste pipe. Water Corporation says fats, oils and grease cause about 30% of wastewater blockages. Wipe pans, bin leftover oil, and use a sink strainer. If it keeps happening after a clear, the plug may be further down the line.
Can I tip boiling water or chemicals down a blocked sink?: Boiling water alone rarely clears a real grease plug and can crack porcelain. Caustic or acid drain cleaners are worse: they sit in the pipe, can burn skin if the sink backs up, and make the plumber’s job unsafe. Bail, plunge, or call us.
My sink and dishwasher are both backed up. Is that one job?: Usually yes — they often share the same waste. Clear or call before running another dishwasher cycle, or you’ll flood the sink.
The bathroom is slow as well. Is that still a sink problem?: No. If more than one area of the house is slow, or the outdoor overflow relief gully is full, the blockage is further down the property sewer. Stop using water and call (08) 6187 3999 or text 0406 882 648. Call Water Corporation on 13 13 75 as well if sewage is overflowing.
Do you clear blocked bathroom vanities and laundry troughs too?: Yes. Hair and soap in a vanity, or lint in a laundry trough, are the same kind of local waste-pipe job. Tell us which room when you book.

Official sources

Last updated 13 October 2026. General information only. Every property is different, so call us to talk about yours.

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