Why is my drain blocked? Causes, what to try first, and when to stop

TL;DR

A blocked drain is usually caused by fat, wipes, hair, or root intrusion narrowing the pipe until water can no longer get past. If you’re dealing with a slow or gurgling drain, try these in order: a plunger over the affected outlet, then hot water with washing-up liquid poured down slowly to help break up grease, then a drain auger if you have one, and stop and get help if more than one fixture is affected or an outside gully is surcharging, because that usually points to a blockage further down the system than DIY tools can reach. If you’ve reached that point, request help through our online form and we’ll take it from there.

The symptoms that tell you what you’re dealing with

Not every slow drain is the same problem, and the symptoms are a useful guide before you reach for anything:

• Gurgling from a plughole or toilet when another fixture is used. This is a sign air is being trapped and pushed back through the system, usually because something downstream is restricting flow.
• One sink or bath draining slowly. Often a fairly local blockage close to that fixture, commonly fat, soap scum or hair.
• Multiple fixtures backing up at once, such as water rising in the bath when you flush the toilet. This points to a blockage further down the shared pipework, past the point where the individual fixture wastes join.
• An outside gully surcharging, meaning water pooling or overflowing around an outside drain cover, especially near the kitchen. This usually means the blockage is beyond that point, in the underground run towards the sewer connection.

The further from the affected fixture the real problem sits, the less a plunger under the sink is going to achieve, and the more likely you’re looking at something that needs a drain rod, an auger, or a proper look with a camera.

What to try first, in order

For a single slow-draining fixture with no other symptoms, this is a sensible order to work through:

1. Plunger. Cover the overflow if there is one, and use a cup or flange plunger directly over the plughole or outlet with enough water in the basin to create a seal. A few firm pumps often shifts a local blockage.
2. Hot water and washing-up liquid. Add a good squeeze of washing-up liquid to the drain, then follow it with hot water poured slowly. Use very hot water rather than boiling water straight off the kettle: boiling water can crack a ceramic bowl or basin, and it can also soften and deform the uPVC or ABS trap and waste pipe fitted under most modern kitchen sinks, which is exactly where a fat blockage tends to sit. The washing-up liquid helps break down grease build-up so the hot water can carry it through. Avoid this step altogether on a fully blocked toilet, or where standing water suggests the pipe is already completely obstructed, since the water has nowhere to go.
3. Drain auger (also called a plumber’s snake). For a blockage a plunger can’t shift, a hand-cranked auger fed down the waste pipe can physically break up or hook out the obstruction, typically hair, wipes or a solid clump of debris.
4. Stop. If none of the above clears it, or the symptoms point to a shared or mains-side blockage rather than something local, it’s time to stop and get it looked at properly rather than escalating the tools you’re using.

What not to do

Caustic soda-based drain cleaners are widely sold as a DIY fix, but they’re worth being cautious about, particularly in Northampton’s older housing stock. A lot of the Victorian terraces built during the town’s shoe-industry years, around Abington and Far Cotton, and many of the streets off the Wellingborough and Kettering Roads, still have original clay drainage. Repeated use of strong caustic chemicals can degrade ageing pipe joints and seals over time rather than genuinely fixing the underlying blockage. They can also generate significant heat in the pipe and are unpleasant and risky to handle if a blockage means the chemical doesn’t clear and sits in standing water. If a blockage needs more than washing-up liquid and hot water, a mechanical clear or a proper blocked drains visit is a safer route than reaching for something stronger from under the sink.

When to stop and get help

A few signals reliably mean the problem is beyond what a plunger or auger under the sink can fix:

• More than one fixture is affected, especially if they’re on different floors or different parts of the house. This points to a shared drain run rather than an individual waste pipe.
• An outside gully or manhole is surcharging. Water backing up outside the property means the blockage is in the underground drain, not the internal pipework.
• The blockage keeps coming back at the same spot despite repeated clearing. That’s usually a structural issue like a root intrusion or displaced joint rather than a one-off, and it’s worth a proper look with a CCTV drain survey to see exactly what’s happening inside the pipe.
• It’s affecting your only toilet, or waste water is backing up into the house. At that point it’s no longer a DIY job to wait out, and our emergency plumber service is there for exactly this kind of situation.

Frequently asked questions

Why does my drain keep blocking?

A drain that blocks repeatedly in the same place, rather than as an occasional one-off, usually has an underlying cause: root intrusion from a nearby tree or hedge, a displaced pipe joint, a section with poor fall that lets debris settle, or ongoing fat build-up from a kitchen waste. Clearing the blockage each time treats the symptom; a CCTV survey identifies the actual cause so it can be fixed properly rather than repeated.

Can I pour drain cleaner down an outside drain?

We’d advise against strong caustic cleaners in outside gullies and drains, particularly on older properties with original clay pipework, for the same reasons as indoors: they can degrade ageing joints over time and are hazardous to handle if the blockage doesn’t clear straight away. Outside gullies are also often shared or lead directly to the wider sewer network managed by Anglian Water across Northampton, so a chemical poured down one that doesn’t fully clear can sit for longer than you’d expect.

Still blocked? Get it sorted properly

If you’ve worked through the plunger, hot water and auger and the drain is still slow, gurgling, or backing up, it’s time to stop guessing. Request help through our online form with a description of what’s happening and which fixtures are affected, and we’ll advise whether it needs a straightforward clear or a closer look with a camera. If the blockage is affecting more than one fixture or your only toilet, don’t wait it out; get in touch and tell us that in your message so we can plan around it.