How to tell your outside drain is blocked
An outside drain is the external gully or manhole that carries wastewater away from your kitchen, bathroom and downpipes into the main sewer. When it blocks, the signs usually appear inside the house first: sinks that drain slowly, gurgling from the toilet when you run a tap elsewhere, or an unpleasant smell drifting up from the plughole.
The clearest confirmation is outside. Lift the cover on the nearest manhole or gully at the side or back of the property. If it's full of standing water or debris right up to the top, the blockage is between that chamber and the main sewer. If it's empty but the chamber further upstream is full, the blockage is somewhere between them.
What causes external drains to block
In most Northamptonshire homes we get called out to, the cause is one of four things: fat and food waste that solidifies in the pipe after being poured down the kitchen sink; wet wipes, sanitary products and other items that shouldn't be flushed but often are; a build-up of leaves, silt and moss washing down from gutters into the gully; or tree root intrusion, which is especially common in older Victorian and Edwardian clay pipework where roots find their way in through the joints.
Recurring blockages are almost always a sign that one of these underlying causes hasn't been dealt with — clearing the immediate blockage helps for a few weeks, but the same thing builds up again.
What you'll need before starting
Before you attempt to clear it, put on heavy-duty rubber gloves and old clothes you don't mind ruining. Have a bucket, an old towel and a strong pair of drain rods to hand — you can buy a set of screw-together rods with a plunger and corkscrew head from any DIY shop for around £25. Don't use bleach or caustic chemical drain cleaners on external drains: they rarely shift a real blockage, they're dangerous around your skin, and they make life much harder for a professional if you end up calling one anyway.
Step-by-step: clearing the blockage
1. Lift the drain cover using a screwdriver as a lever if needed, and set it aside safely. Wear gloves — the underside is not pleasant.
2. Screw the rods together as you go, attaching the plunger head first. Feed them down into the drain in the direction of the blockage — that's away from the house, towards the main sewer.
3. Push and pull the rods, rotating them clockwise as you go. Only ever rotate clockwise — if you rotate anticlockwise, the sections can unscrew inside the pipe, and now you have a blockage and a stuck set of rods.
4. You'll usually feel the blockage give way — the water level in the chamber will drop quickly. Once it clears, run a hose or several buckets of water through to flush the line.
5. If plunging doesn't shift it, swap the plunger head for the corkscrew attachment and try again — this is better for solid material like wet wipes or root debris.
When to stop and call a professional
There are three situations where DIY becomes the wrong tool: you can't reach the blockage with rods (usually more than about 4 metres in); the blockage keeps returning within days or weeks; or you can see sewage backing up into the property. In any of those cases, keep going and you'll usually just spread the problem further down the line — or damage the pipe.
A professional will use CCTV to see exactly where the blockage is and what's causing it, then either high-pressure jet it clear (which cleans the full pipe wall, not just a channel through the middle) or, if a section has collapsed or been damaged by roots, quote for a patch repair or lining. That's a lot cheaper than digging up your driveway to find out what's wrong.
If your property is in Northamptonshire or one of the surrounding counties we cover, our first-hour visit is a fixed £300 and includes diagnosis, rodding or jetting where suitable, and a CCTV camera check within that first hour if we need one — no hidden camera fee.
How to stop it happening again
Never pour fats or oils down the kitchen sink — let them cool and put them in the bin. Only flush the three P's (pee, paper, poo) — wet wipes labelled 'flushable' are one of the biggest single causes of blockages we see. Clear leaves out of gutters at least once a year to stop them washing down into gullies. And if you have a large tree within about 10 metres of your drain run, particularly on an older property with clay pipework, consider a one-off CCTV survey — catching root intrusion early is a lot cheaper than dealing with a collapsed pipe later.
FAQs
Should I use bleach or a chemical drain cleaner first?
No. Chemical cleaners rarely clear a real external blockage, they're dangerous around your skin and eyes, and they make the job more hazardous for anyone who has to work on the drain afterwards. Skip straight to drain rods.
How much does it cost to have an outside drain unblocked professionally?
Our fixed-price first-hour visit is £300, covering diagnosis, rodding or jetting where suitable, and a CCTV camera check if needed within that first hour. Most straightforward blockages are cleared within that time.
Who is responsible for a blocked outside drain — me or the water company?
As a rule of thumb, drains that only serve your property are your responsibility. Shared sewers that serve more than one property are usually the water company's responsibility. If we identify a blockage as their responsibility, we'll tell you before quoting for any private work.
Can I damage the pipe by rodding too hard?
Modern PVC pipework is fairly resilient, but older clay pipes can crack if you force rods against a hard blockage or root mass. If the rods aren't shifting it after a few minutes of steady work, stop — call someone in with a CCTV camera and jetting kit rather than push on and risk breaking the pipe.