Signs it's more than the sink
- Both bowls of a double sink are slow, not just one.
- The dishwasher leaves water in the bottom, or empties back into the sink.
- The gully outside the kitchen is wet or smells.
- The laundry tub or a shower gurgles when the sink empties.
- The sink cleared, then blocked again within days.
Why kitchen sinks block
Warm fat and oil go down the sink as liquid, then cool and set inside the pipe. Food scraps, coffee grounds and rice catch on that coating, and the pipe narrows bit by bit until it stops.
The trap under the sink is the first place it builds up. In older homes the pipe from the kitchen to the gully outside can be long, and grease can coat all of it.
What a plumber will do
Check under the sink
Look at the trap and waste pipe, and how the dishwasher hose joins them.
Clear the line
Feed a drain machine through to break the blockage, or jet the pipe if grease coats its length.
Check the gully
Look at the gully outside to see whether the blockage reaches that far.
Find the cause
If it keeps happening, run a camera to look for a sag or a damaged section.
What changes the job
- Whether it's the trap alone or the pipe beyond it.
- How long the run to the gully is, and whether it's under the house or in a slab.
- How much grease has built up along the pipe.
- A dishwasher, waste disposal unit or second bowl on the same waste.
- Whether the main drain outside is blocked as well.
What you can do, and what to leave
You can
- Bail standing water into a bucket, so the plumber can see the plughole.
- Scrape plates into the bin, and keep a strainer in the plughole.
- Let fat and oil cool in a container, then put them in the bin.
- In WA, Building and Energy's homeowner list includes "clearing a blocked fixture or waste pipe by using a plunger". Elsewhere, check what you can do yourself.
- Tell the plumber about any drain cleaner you've used, because it can splash when the pipe is opened.
Leave to a licensed plumber
- Taking apart the trap or the waste pipes under the sink.
- Drain machines and jetting.
- The dishwasher's drain connection: see appliance plumbing.
- Anything past the sink: the gully, the main drain or a broken pipe.
Licences and paperwork
A sink waste is sanitary plumbing. In WA, apart from plunging and a few other jobs on the homeowner list, work on it "must be carried out by a licensed plumber or permit-holder".
If the fix turns into new pipework, ask about paperwork. In NSW, minor works such as "replacing tap ware" don't need a Notice of Work, but most other plumbing and drainage work needs one before it starts and a Certificate of Compliance when it's done. Planning a new kitchen? See kitchen and bathroom plumbing.
Red flags
- Says the whole drain needs replacing without showing you camera footage.
- Offers a chemical treatment as the only answer to a sink that keeps blocking.
- Ignores the dishwasher when it's clearly part of the problem.
- Can't give you a licence number for the state you're in.
What we would do
If it's one sink and you know it's grease, a plumber with a drain machine should have it running again in one visit. If it keeps coming back, ask for the pipe to be jetted rather than just punched through, and change what goes down the sink. For anything beyond the trap, a drain specialist can tell you whether the pipe itself is the problem.