A slow draining sink or a gurgling shower is usually the first sign of a blocked drain building up in your waste pipes. The good news is that most household blockages can be cleared quickly without calling a drainage specialist. This guide shows you how to unblock a drain indoors and outside, how to clear a blocked sink or shower, and how to stop drains smelling.

What causes a blocked drain?

Most blockages are caused by fat, grease, food waste, hair, soap scum and other organic matter that sticks to the inside of the pipe. Over time this narrows the pipe until water can no longer flow freely. Outside drains and gullies also block with leaves, silt and garden debris, especially in autumn.

How to unblock a sink or shower drain

Start with the simplest methods and work up:

1. Hot water. For a minor grease blockage, pour a kettle of very hot water down the drain to soften and shift it. Let it cool slightly first if you have plastic pipes.
2. Plunger. A cup plunger creates suction that can dislodge a nearby blockage. Block the overflow with a damp cloth first for a better seal.
3. Clean the trap. The U-bend under your sink often traps debris. Put a bucket underneath, unscrew the trap and clear it out. This is also the simplest way to clean a sink drain.
4. Drain snake. To use a drain snake, feed the coiled end into the drain, turn the handle as you push until you feel resistance, then keep turning to break up or hook the blockage and pull it out. It’s particularly good for hair in showers and basins.
5. Drain unblocker. When the blockage is further down the pipe or won’t shift, a chemical drain unblocker dissolves the build-up.

Can you unblock drains naturally? Home remedies such as bicarbonate of soda and vinegar can freshen a drain and may help with very light, slow-draining build-up, but they’re much milder than a purpose-made drain unblocker. For a stubborn blockage, move on to the steps above.

Using a caustic drain unblocker

A sodium hydroxide (caustic soda) drain unblocker such as Bond-It Drain Blaster is a fast way to clear stubborn fat, grease and hair blockages. It sinks through standing water to reach the blockage, dissolves it in around 15 minutes and kills the germs that cause bad smells.

1. Pour in the recommended amount.
2. Leave it to work (overnight for tough blockages).
3. Flush through with hot water.

Safety: wear gloves and eye protection. Never mix a drain unblocker with other drain products or bleach. Never use a caustic unblocker in a toilet, waste disposal unit or septic tank. If the water hasn’t cleared, don’t plunge a pipe that still has chemical standing in it, as it can splash back.

How to unblock an outside drain

Wondering how to unblock an outside drain or gully? Follow these steps:

1. Lift the grid and clear any visible debris by hand, wearing gloves.
2. If the blockage is deeper, push a set of drain rods through the pipe to break it up.
3. For grease and organic build-up in the pipe run, pour a caustic drain unblocker directly into the chamber.
4. Flush through with water.

If the water still won’t drain and the blockage is on the main sewer side, it may be a shared or public sewer. Contact your water company.

How to stop drains smelling

Drain odours are caused by trapped food, grease and bacteria decomposing in the pipe. The most reliable fix is to remove the build-up: a weekly maintenance dose (around 100 ml) of drain unblocker keeps pipes clear and removes the source of the smell. Also make sure every trap holds water, because a dry trap lets sewer gas back into the room. Run water through rarely used sinks, showers and floor drains every week or two.

When to call a plumber

If you’ve tried plunging, cleaning the trap and a chemical unblocker and the water still won’t drain, or if several fittings back up at once, the blockage may be in the main soil pipe. This is best left to a professional drainage specialist.

How to keep drains clear

Prevention is easier than cure:

• Don’t pour fat or oil down the sink.
• Use a plughole strainer to catch hair and food.
• Run a maintenance dose of drain unblocker through your sinks once a week.

For plumbing and heating system cleaning, the PC400 flushing chemical and PC300 system cleaner keep pipework and radiators running efficiently.

FAQs

How do I unblock a sink drain?
Try hot water, then a plunger, then clean the trap. If the blockage is further down the pipe, use a drain snake or a caustic drain unblocker.

How do I stop my drain smelling?
Remove the build-up causing the odour with a weekly maintenance dose of drain unblocker, and keep your traps full of water.

What’s the best way to unblock an outside drain?
Clear visible debris by hand, then use drain rods or pour a drain unblocker into the chamber.

Can I use a drain unblocker in a toilet?
No. Never use a caustic drain unblocker in a toilet, waste disposal unit or septic tank.

Always read the product label and follow the safety instructions before using any drain-cleaning chemical.