Why Does My Sink Keep Getting Blocked? | BLDESY
You've cleared the kitchen sink twice this month and it's already draining slow again. A one-off blockage is annoying — a sink that keeps blocking is your pipes telling you something, and it's worth knowing what before you keep pouring chemicals down there.
The short answer
A sink that blocks once is usually just gunk near the plughole. A sink that keeps blocking — same spot, every few weeks — means the buildup is further down the pipe than a plunger can reach, or something structural is slowing the water enough that everything sticks to it. The fix depends on which one it is, and the difference is usually easy to tell from what you're seeing.
What's actually causing it?
Kitchen and bathroom sinks block for different reasons, so start with which one you've got.
Kitchen sink. Almost always fat, oil and grease. It goes down warm and liquid, then cools and hardens against the inside of the pipe like candle wax. Every wash after that sticks to what's already there — coffee grounds, rice, vegetable peelings — until the opening is narrow enough to catch everything that follows.
Bathroom sink. Usually hair mixed with soap scum. Hair catches on the drain's crossbar or the edge of the trap, soap scum binds to it, and the clump grows a little with every shave or wash until it's blocking most of the pipe.
Either sink, if it keeps happening. The P-trap — the U-shaped bend under the sink — is the usual first checkpoint. If you've cleared that and it's still recurring, the blockage has probably moved further along the branch line. In older homes, especially anything with clay or cast-iron drainage from before the 1980s, tree roots finding a hairline crack underground are a genuine and common cause of a sink that blocks on a schedule.
How often is "too often"?
One blockage in two years isn't a pattern — that's normal wear, and a plunger or a trap clean should sort it. The pattern worth paying attention to is the same sink, blocking on a rough cycle — every few weeks, or worse, every time you run a load of washing or a long shower. That regularity is the signal. It means whatever's slowing the water is still there after you clear the symptom, and it's rebuilding at roughly the same rate each time.
What can I safely try myself?
Before you call anyone, these are worth doing in order:
- Boiling water, in stages. Pour a kettle-full down slowly, wait a few minutes, repeat. Works well on grease, does almost nothing for hair clumps.
- A proper plunge. Block the overflow hole with a wet cloth first — otherwise you're just moving air around, not building pressure — and plunge in short, sharp strokes rather than one long push.
- Clean the P-trap. Put a bucket underneath, unscrew the trap by hand or with pliers, and physically clear what's sitting in the bend. This solves the problem more often than anything you can pour down the drain.
- A drain snake or a cheap plastic zip-it tool. Feeds a metre or so down the pipe and pulls hair clumps out rather than pushing them further along, which is what plungers tend to do.
What should I avoid doing?
Repeated use of caustic drain cleaners is the biggest mistake people make. They can clear a blockage once, but the chemical reaction generates heat, and repeated use can soften or crack older plastic pipework — which turns a free DIY fix into a pipe replacement. If the first attempt with one doesn't clear it, stop and move to a mechanical method instead of pouring more down.
Wire coat hangers are the other common mistake — they're rigid enough to scratch the inside of the pipe or puncture an older joint, which creates a slow leak you won't notice until it's a bigger problem than the blockage was.
When is it more than a DIY problem?
A few signs mean the blockage is beyond what a plunger or a trap clean will fix:
- It's the same sink, every few weeks, even after you've cleared the trap yourself.
- More than one fixture is affected at once — the toilet gurgles when the sink drains, or the shower backs up when the washing machine's running. That points to the shared line further down, not the fixture itself.
- There's a persistent bad smell from the drain even when the water's running clear.
- The whole house drains slowly, not just the one sink.
Any of those point to something in the main line rather than the fixture — root intrusion, a partial pipe collapse, or a genuine pitch problem in older plumbing. That's not something a plunger fixes, and pushing harder on DIY at that point usually just delays a bigger job.
What does a plumber actually do differently?
Past the P-trap, a plumber has tools you don't. A drain camera shows exactly what's blocking the line and where, so nobody's guessing. A hydro-jetter clears the full diameter of the pipe with high-pressure water, rather than punching a single hole through the blockage the way a hand snake does. For root intrusion specifically, that's the difference between a fix that lasts a year and one that lasts a fortnight.
How do you stop it happening again?
Once it's cleared, the habits that actually prevent a repeat are simple:
- Kitchen: wipe pans out with paper towel before washing, and bin fat rather than pouring it down warm. A basic sink strainer catches the solids that would otherwise build the first layer.
- Bathroom: a cheap hair catcher over the plughole, cleared weekly, stops most bathroom blockages before they start.
- Both: a monthly hot water flush is a five-minute habit that keeps grease and scum from building up between the times you're actively cleaning the trap.
Getting someone in who's actually qualified
If you've got to this point, the job's moved from a five-minute fix to letting someone into your house with tools — and that's worth doing properly. Plumbing work in NSW always requires a current licence, regardless of the job size; there's no small-job exemption the way there is for some other trades. It's worth a quick check before anyone arrives, not after.