You clear it, it drains for a week or two, and then it’s back. Water sitting in the sink, a funky smell and that slow, sad gurgle as it finally drains away.
If your kitchen sink keeps blocking, the good news is that the cause is usually one of a handful of common problems. The bad news is that most quick fixes only treat the symptom, so the blockage comes straight back.
Here are the seven most common reasons a kitchen sink keeps blocking, what you can safely try yourself and when it’s time to get a plumber to take a proper look.
1. Grease and fat build-up
This is the number one cause of blocked kitchen sinks. When you pour oil, fat or greasy water down the drain, it’s liquid while it’s warm. As it cools inside the pipe, it hardens and sticks to the pipe walls.
Each time you wash up, a little more builds up. Food scraps then get caught in that sticky layer until the pipe narrows so much that water can barely get through.
The fix: Wipe greasy pans with paper towel before washing them and put cooled fat in the bin. If the build-up is already bad, high-pressure jetting is the most effective way to clean it out.
2. Food scraps
Rice, pasta, coffee grounds, eggshells and vegetable peelings are all regular culprits. Rice and pasta swell with water, coffee grounds clump together, and eggshell fragments act like sand in the pipe.
The fix: Use a sink strainer and empty it into the bin or compost. It’s the cheapest plumbing upgrade you’ll ever make.
3. Soap scum
Some soaps contain fats that react with minerals in the water to create a hard, chalky residue. Perth’s hard water can make this worse. Over time, soap scum combines with grease to form a stubborn coating inside the pipe.
4. A problem with the trap
The trap is the curved section of pipe under your sink. It holds a little water to stop sewer smells coming up, but it’s also where debris collects.
If something solid has fallen down the plughole, like a bottle cap or a piece of cutlery, it can get stuck in the trap and catch everything that follows.
5. Poor pipe fall or a dip in the line
Drain pipes need a slight downhill slope, called fall, so water and waste can flow away. If a pipe was installed with too little fall, or a section has sagged, water sits in the low spot and waste settles there.
This is common after kitchen renovations where the sink has been moved, and it’s a classic reason a sink keeps blocking no matter how often it’s cleared.
6. Tree roots further down the line
If your kitchen sink drains into a sewer line that runs past trees, roots may be growing into the pipe further along. This is especially common in older Perth suburbs with clay sewer pipes.
A clue is when other fixtures, like the laundry tub or shower, are also draining slowly, or the outdoor gully trap overflows.
7. A damaged or collapsed pipe
Older pipes can crack, shift or partly collapse. Waste catches on the broken section and the blockage keeps returning. Only a camera inspection will show this for sure.
What you can safely try at home
For a slow sink, these simple steps are worth a go:
- Remove and clean the sink strainer and plug.
- Pour a kettle of hot (not boiling) water down the drain to soften grease. Avoid boiling water if you have plastic pipes.
- Use a sink plunger, covering the overflow hole with a damp cloth to create better suction.
- If you’re confident, put a bucket under the trap, undo it by hand and clear out any debris.
We don’t recommend harsh chemical drain cleaners. They rarely clear serious blockages, they can damage some pipes and they make the job more hazardous for whoever has to clear it next.
Double sinks and dishwashers
If water rises in one bowl when the other drains, or the sink fills when the dishwasher empties, the shared waste pipe below is partly blocked. Clearing just one side won’t fix it. The blockage needs to be cleared where the pipes join, or further down the line.
When to call a plumber
It’s time to call in a professional if:
- The sink blocks again within a few weeks of clearing it
- Other drains in the house are slow too
- Water comes up in another fixture when the sink drains
- There’s a bad sewer smell that won’t go away
- Your outdoor gully trap is overflowing
A plumber can clear the blockage properly with a drain machine or water jetting, then run a camera through the pipe to find out exactly why it keeps happening.
Kitchen sink still blocking?
If your kitchen sink keeps blocking, it’s time to fix the cause, not just the symptom. Call Your Plumbing Pros on 08 6118 4273 or book a blocked drain visit and we’ll get to the bottom of it.
Frequently asked questions
Can I pour boiling water down a blocked sink?
Hot water can help soften grease, but boiling water can damage plastic pipes and fittings. Use hot tap or kettle water that’s just off the boil instead.
Does baking soda and vinegar unblock drains?
It can freshen a drain and help with very minor build-up, but it won’t clear a real blockage caused by grease, roots or a damaged pipe.
How much does it cost to unblock a kitchen sink in Perth?
It depends on where the blockage is and what’s causing it. A plumber will assess it and confirm the cost before starting work.
Why does my sink smell even when it’s not blocked?
Smells usually come from food and grease build-up in the trap or pipe, or a dried-out trap that’s letting sewer gas through.
Is a sink strainer really worth it?
Yes. A strainer catches food scraps before they reach the pipe and is one of the cheapest ways to prevent kitchen sink blockages.