A kitchen sink that drains slower and slower, with water pooling in the basin and refusing to clear, is usually caused by grease and food waste building up on the inside of the drain pipe, narrowing the passage more and more. In the early stages, hot water with dish soap or a few pushes with a plunger will usually sort it out; but if it has stayed slow for weeks with no improvement, and even gives off a foul smell, it means the grease has built up thick, and you need professional high-pressure water jetting to clear it properly.
Why Does a Kitchen Sink Drain Slower and Slower?
Unlike a toilet that suddenly clogs solid, a slow kitchen drain is mostly a "gradual buildup" problem. Common causes include:
- Grease buildup — this is the number one culprit behind a slow kitchen drain. Greasy water from washing woks and dishes flows into the pipe, cools and sticks to the inner wall, and over time forms a film of grease that narrows the passage.
- Food scraps, rice grains and tea leaves wash down the drain and tangle up with the grease, forming a thick, solid blockage.
- No strainer fitted, or one that is never cleaned, letting debris go straight into the pipe.
- A silted-up trap (U-bend) — the U-shaped bend under the sink most easily traps debris.
- Silting in the downstream main drain of older buildings or village houses, which slows the whole line.
Immediate Self-Help Steps for a Slow Kitchen Drain
- First scoop out or drain the water pooled in the basin, and clear the debris off the strainer.
- Pour one or two tablespoons of dish soap into the drain, then slowly add a kettle of hot water (use hot, not boiling — boiling water can deform plastic pipes and joints), and wait about ten-odd minutes to let the grease soften.
- Fill the drain with a little water, seal a plunger over it and push and pull firmly a few times, using pressure to loosen the blockage.
- If you know how, put a bucket under the sink, unscrew the trap to clean out the sludge inside, and screw it back tightly.
- If it still won't clear after all this, stop — don't add more chemicals or poke around with hard objects, as this easily damages the pipe joints.
What You Shouldn't Do
- Don't keep pouring in drain cleaner. Strong acid or alkali cleaners are of limited use on thick grease, and the residue corrodes the pipe joints — overusing it harms the pipes and your hands.
- Don't pour boiling water into PVC plastic pipes. The high heat softens and deforms the pipe and joints, and can cause leaks.
- Don't force apart pipes you don't understand. A trap that isn't reassembled tightly will leak — not worth it.
When Should You Call a Professional?
- You've tried hot water, the plunger and cleaning the trap, but it's still slow or quickly goes slow again.
- Multiple drainage points — kitchen, toilet, floor drain — all drain slowly at once, meaning the blockage is in the main drain rather than a single spot.
- In a commercial kitchen or food premises, a slow drain is usually linked to a silted grease trap or grease line, so the scope is large.
- In an older building or village house, you suspect the downstream pipe or septic tank is silted up.
In cases like these, drain cleaner is almost useless. You need professional high-pressure water jetting to flush away the thick grease, and if necessary a CCTV pipe survey to locate the blockage, so it can be resolved thoroughly and won't go slow again soon after clearing.
How to Prevent a Slow Kitchen Drain?
- Fit a strainer and bin the rice grains, vegetable scraps and tea leaves rather than washing them down the sink.
- Don't pour used cooking oil into the sink — letting it cool and wiping or tipping it into a container to bin is the most effective prevention.
- Regularly flush the drain with hot water and dish soap to wash grease away before it sets hard.
- Have shops and food premises clean the grease trap regularly — don't wait until the whole grease line is blocked before dealing with it.
FAQ
Q: Can I use drain cleaner on a slow kitchen drain? It may help a little with a thin grease film or a minor blockage, but it is of limited use against thick grease and deep blockages, and the chemical residue corrodes the pipes, so don't rely on it long term.
Q: Can I pour boiling water into the kitchen drain? Not advisable. Boiling water softens and deforms PVC plastic pipes and joints, and can even cause leaks. To flush grease, warm or hot water with dish soap is enough.
Q: Is a strainer really useful? Yes. A strainer stops solid debris like rice grains and vegetable scraps from entering the pipe, reducing the tangling with grease that forms blockages — it's the simplest and most effective prevention.
Motion Waste Management Limited (Drainage Services Department (DSD) registration number P0038) has served all of Hong Kong since 1992, providing drain clearing, kitchen grease-line and grease trap cleaning, high-pressure water jetting and CCTV pipe survey services. If you can't fix a slow kitchen drain yourself, you can first describe the situation via WhatsApp or the quotation form; we assess first then quote, with transparent pricing, to help you get back to normal as soon as possible.