Blocked Kitchen Sink? Here’s What You Should Never Pour Down the Drain

A blocked kitchen sink is one of the most common household issues—and one of the most preventable. While it might seem harmless to rinse food scraps or grease down the sink, these everyday habits are often the root cause of blocked drains.

Many homeowners don’t realise the damage they're doing until it’s too late, requiring costly drain unblocking or even full drain surveys to locate the problem. In this blog, we'll explore the most common culprits behind blocked kitchen sinks and what you should always avoid pouring down the drain.

1. Cooking Oil and Grease

One of the worst offenders is cooking oil and grease. After frying or roasting, it might seem convenient to wash oily pans directly in the sink. But as the oil cools, it hardens and sticks to the inside of your pipes. Over time, this creates a thick, sticky sludge that traps food particles and causes serious blockages.

Even mixing grease with hot water or soap doesn’t fully solve the problem—it simply moves the blockage further down the pipe. The result? You’ll likely need professional drain services to clear the mess.

What to do instead: Pour cooled grease into a container (like an old jar), seal it, and dispose of it with your general waste.

2. Coffee Grounds

You might assume that because coffee grounds are small and gritty, they’ll just wash away. But when wet, they clump together and settle in bends and joints in your plumbing. Combined with grease or food particles, they quickly contribute to blocked drains.

Coffee grounds are surprisingly absorbent and can act like a sponge inside your pipes, slowing drainage and eventually stopping it altogether.

What to do instead: Toss coffee grounds into your compost bin or use them in your garden as a natural fertiliser.

3. Pasta, Rice and Starchy Foods

Starchy foods like pasta, rice, and potatoes are notorious for expanding when wet—and they don’t stop once they’ve gone down the drain. These foods turn into a sticky paste that clings to pipe walls and traps other debris, leading to tough blockages that require drain unblocking.

Even small leftovers can collect and cause problems over time, especially in homes where sink strainers aren't used regularly.

What to do instead: Scrape food scraps into the bin before rinsing plates, and consider using a fine mesh strainer over your plughole.

4. Food Scraps and Eggshells

While many people have a “rubbish sink”, using it to dispose of food scraps and eggshells is a fast track to trouble. These materials don’t break down easily, and eggshells can even sharpen into tiny shards that catch in your pipes.

Some food scraps, like fibrous vegetables (e.g., celery or onion skins), can tangle and clump together, turning a slow drain into a full blockage that may require a drain survey to diagnose if it’s not immediately visible.

What to do instead: Use a food waste caddy or compost bin to dispose of scraps, and keep your drain clear with regular rinsing using boiling water.

5. Flour and Dough

Flour may seem harmless, but when mixed with water, it forms a sticky paste that solidifies inside your plumbing. If you’re baking or cooking, avoid rinsing large amounts of flour or dough into the sink.

Once hardened, these substances create solid clumps that can completely block narrow sections of your pipes, especially in older plumbing systems. They’re difficult to remove without the help of professional drain services.

What to do instead: Wipe excess flour or dough from mixing bowls with a paper towel and discard it in the bin before washing.

6. Cleaning Products and Harsh Chemicals

Believe it or not, not all cleaning products are safe for your drains. Harsh chemicals like bleach, drain openers, and antibacterial cleaners can damage pipe linings and disrupt the natural bacterial balance in your plumbing system.

If you’re already dealing with blocked drains, adding more chemicals could worsen the situation or push the blockage further down the line, making it more difficult to reach without advanced drain surveys.

What to do instead: Use enzyme-based cleaners for routine maintenance or contact a professional for safe, effective drain unblocking.

When to Call the Experts

If your sink is draining slowly or emitting a foul smell, these could be early signs of a more serious issue. Persistent problems often indicate a deeper blockage that home remedies won’t fix. In such cases, a qualified technician can carry out a drain survey using CCTV equipment to pinpoint the problem and provide targeted drain services.

Mobile drain unblocking teams can often respond quickly, saving you time, stress, and the risk of long-term damage to your plumbing.

Final Thoughts

The kitchen sink isn’t a rubbish bin—what goes down your drain today could be tomorrow’s plumbing problem. Avoid pouring oil, coffee grounds, starches, and other common cloggers down your sink to prevent blocked drains and costly repairs.

When prevention fails, professional drain unblocking and drain services are your best bet for a fast, safe solution. And if you’re unsure of the source of the problem, a detailed drain survey can help identify the cause before it turns into a plumbing disaster.

Stay smart with your sink, and your pipes—and wallet—will thank you.