Compare the trap with the outside gully before choosing access. On blocked sink and kitchen drains, that comparison shows whether the restriction ends below the sink or continues along a grease-lined branch.
Switch off any dishwasher or washing machine feeding the same waste pipe before opening the trap. Note whether the outside gully also rises, because that separates a local sink restriction from grease farther along the run.
Clearing sinks and kitchen waste pipes
The trap under the sink gets the blame, but the build-up often runs much further than that.
A tool can make a narrow hole through soft grease and produce a brief improvement while most of the deposit remains on the pipe wall. The useful question is how much of the affected waste run has actually been cleaned.
The trap, horizontal waste pipe and outside gully are checked as one route. Where the deposit continues beyond the sink, stopping at the first free-flowing point leaves the cause in place.
Pulling the trap apart clears the first metre. A greasy pipe needs its full length dealt with, which is where drain jetting comes into its own.
When the sink clears but the outside gully remains full
Grease can line the waste pipe between the sink and the outside drain. Piercing a soft plug near the bowl may empty the sink briefly while the longer branch remains restricted.
The kitchen branch needs an accessible route and somewhere for loosened grease to be collected. A flow check should include the outside gully rather than relying on the sink alone.
Ask whether the shared waste pipe was checked
Clearing the sink trap is not enough when another appliance or the outside gully reacts at the same time. The connected branch then needs checking as one run.
Are you clearing the trap, or the whole run to the drain?
Will the grease be removed, or just pierced?
Does the outside gully need attention at the same time?
Is the smell coming from this blockage or from a dry trap elsewhere? Our bad drain smells page covers the difference.
What habits would stop this recurring, honestly stated?
If your kitchen sink drains slowly but never quite blocks, that pattern has its own page: slow draining water explains what the sluggishness means.
Why kitchen drain blockages come back
A sink may begin moving again after a small channel opens through cooled fat. The rest of the deposit can remain on the pipe wall and start catching food almost immediately. Repeated use of strong products can hide that pattern for a while without cleaning the full run.
Look beyond the trap when the symptoms suggest a longer restriction. That can include the waste pipe through the wall, the outside gully and the underground connection. For prevention, scrape plates, collect cooled fats and keep a strainer over the plughole. Our blocked drain prevention advice covers the everyday habits that protect kitchens and bathrooms.
Caustic drain products keep it moving. Why stop? They dissolve a channel through the grease and leave the rest lining the pipe, so the blockage rebuilds faster each time. Our guide to when drain cleaner is the wrong choice covers those warning signs before someone has to work on a pipe full of caustic residue. We run a commercial kitchen. Is this different? Yes, mainly in volume. Commercial fat loads overwhelm domestic-style pipework quickly, and a planned degrease beats emergency closures. See our restaurant drain unblocking page.
Can fat from my kitchen block the drain in the road? It contributes, yes. Fat from many kitchens combines in sewers into hard deposits, which is why water companies campaign against pouring it away. Cooled fat belongs in the bin.