You can usually unblock an outside drain yourself by lifting the drain covers, finding which chamber is full, and pushing drain rods with a plunger head along the pipe towards the blockage until the water drains, then flushing it through with a hose. If the drain is shared with neighbours or the blockage is beyond your boundary it is normally the water company’s job, and if rods will not shift it or it keeps coming back, it is time for a drainage engineer.

Signs your outside drain is blocked

A blocked drain outside the house usually shows itself in more than one place. Look for:

• Water pooling around a gully or overflowing from a drain grate
• Sinks, showers and baths draining slowly, often several at once
• Toilets that fill higher than normal when flushed, or gurgle
• A sewage smell outside or coming back up plugholes
• Water or waste visible when you lift a manhole cover

If only one sink is slow, the problem is probably in that waste pipe, not the outside drain. If several fittings are slow or gurgling, look outside. A bad smell indoors can have other causes too, covered in our guide to a drain smell in the house.

If you would rather have it cleared quickly and properly, our drain blockage service uses high pressure water jetting, which clears the blockage and cleans the pipe walls so it is less likely to block again soon.

First, check whose drain it is

In England and Wales, since 1 October 2011, shared sewers and the parts of drains that run outside your property boundary have belonged to the local water and sewerage company. As a general rule:

• A drain that serves only your property and sits within your boundary is your responsibility.
• A pipe that carries waste from more than one property, or the part of your drain beyond your boundary, is normally the water company’s.
• Blocked road drains and public gullies in the street are the council’s.

If every chamber on your property is full, including the last one before the boundary, the blockage may be in the shared sewer. Call your water company before you pay anyone. Our article on who is responsible for clearing a blocked drain explains this in more detail.

What you need

• Heavy duty rubber gloves and eye protection
• Old clothes and something to kneel on
• A set of drain rods with a plunger (rubber disc) head, and ideally a corkscrew head
• A screwdriver, lifting keys or a garden spade to lift covers
• A bucket, a hose, and disinfectant for cleaning up afterwards

How to unblock an outside drain, step by step

1. Stop using water indoors. Every flush and tap adds more water to back up.
2. Find the drain covers. Look for the gully where the kitchen waste and downpipes discharge, and the inspection chamber covers, usually rectangular, along the route of the drain.
3. Lift the covers and look inside. Start at the chamber nearest the house and work towards the road.
4. Work out where the blockage is. If one chamber is full and the next one downstream is empty, the blockage is in the pipe between them. If the chamber nearest the house is empty but a gully is overflowing, the problem is in the gully or its short pipe.
5. Clear a blocked gully by hand. Lift off the grate and, wearing gloves, scoop out leaves, silt and fat into a bucket. Then run a hose into it to check it flows.
6. Assemble your rods. Screw two or three rods together with the plunger head on the end.
7. Rod the pipe. Where you can, work from the empty chamber, pushing the rods up the pipe towards the blockage. You can see the pipe opening, and when the blockage clears the water flows away through the chamber. Push and pull firmly, add rods as you go, and keep turning them clockwise only. Turning anticlockwise can unscrew the rods and leave one stuck in the pipe.
8. Swap to the corkscrew head if needed. It helps break up and pull back wipes, rags or roots.
9. Flush it through. Once the water drops, run a hose down the chamber for a few minutes and flush the toilets to check everything runs freely.
10. Clean up. Hose off the rods, disinfect the chamber edges and replace every cover securely.

A note on older homes: the interceptor trap

Many older houses have an interceptor trap in the last chamber before the sewer. It has a U-bend in the chamber base and a short rodding arm sealed with a stopper. If the stopper falls out and lodges in the trap, waste backs up quickly. If your last chamber is full and you can see the rodding arm is open, this is the likely cause. It can be tricky to clear and reseal, so it is often a job for an engineer.

Common causes of outside drain blockages

Cause	What you might notice	Can you fix it yourself?	What the engineer does
Wipes, sanitary items or kitchen roll	Blockage after the toilet, often recurring	Often, with rods and a corkscrew head	Rods or jets the line and checks for a defect that catches debris
Fat and food waste	Slow kitchen gully, greasy build-up	Partly, by clearing the gully	Jets the pipe to remove fat from the walls
Leaves, silt and soil	Overflowing gully after rain	Usually, by hand	Clears and jets the gully and pipe
Tree roots	Repeated blockages, often in older clay drains	No	CCTV survey, cuts roots, and repairs or lines the pipe
Cracked, displaced or collapsed pipe	Blockages keep coming back, damp ground, smells	No	CCTV survey, then patch repair, lining or excavation
Interceptor stopper dislodged	Last chamber full, open rodding arm	Sometimes	Clears the trap and fits a secure stopper or cap

Most of the waste that blocks drains should never have gone down them. Our list of items that should never go down your drain is worth sharing with the household.

What not to do

• Do not use a pressure washer. It can damage older clay joints, and pushes dirty water back at you.
• Do not pour boiling water into plastic drains. It can soften joints. Hot tap water is fine.
• Do not rely on chemicals. Drain unblockers and disinfectants are not designed to shift solid blockages in outside drains, and they make the job hazardous for whoever clears it afterwards.
• Do not keep forcing the rods. If they hit something solid and will not pass, you may be pushing against a collapsed pipe.

When to call a drainage engineer

Call an engineer if the rods will not clear the blockage, if the drain blocks again within weeks, if raw sewage is coming up into the garden or the house, or if you suspect tree roots or a broken pipe. A CCTV drain survey shows exactly what is inside the pipe, so the fix is aimed at the real cause rather than clearing the same blockage again. For out-of-hours flooding, read our guide to emergency drain unblocking.

What it costs with Vantage

In normal working hours there is no call-out fee. After the first hour, time is charged in half-hour steps, and anything extra, such as a CCTV survey or repair, is quoted before we do it. Evening, weekend and overnight visits are charged at the out-of-hours rates. Every rate is published on our prices page, so you know what you will pay before we arrive.

Frequently asked questions

How do I know if the blocked drain is mine or the water company’s?

If the drain serves only your home and the blockage is within your boundary, it is usually yours. If the pipe is shared with neighbours or the blockage is beyond your boundary, it is normally the water company’s, so call them first.

Can I use a plunger on an outside drain?

A sink plunger will not work, but drain rods with a rubber plunger head do the same job inside the pipe. Push and pull the head against the blockage rather than just pushing through it.

Can I use a pressure washer to unblock a drain?

It is best not to. A garden pressure washer lacks the right nozzle for drains, can damage older clay pipe joints and sprays contaminated water back at you. Professional jetting equipment is designed for the job.

Why does my outside drain keep blocking?

Repeat blockages usually mean something in the pipe is catching waste, such as a displaced joint, tree roots, a sag or a build-up of fat. A CCTV survey finds the cause so it can be repaired.

Is a blocked outside drain an emergency?

It becomes urgent if sewage is coming up into the house or garden, or no toilet in the house can be used. Stop using water, keep people and pets away, and get it cleared the same day.

Drain unblocking in Hertfordshire, Bedfordshire and Cambridgeshire

If your outside drain will not clear or keeps blocking, our engineers can jet it clear, survey it with a CCTV camera where needed and tell you exactly what is going on. Visit our drain blockage page or call 01462 506374, answered 24 hours a day, 7 days a week, with 24/7 emergency cover.