To unblock an outside drain, lift the grate, clear debris by hand (gloves on), flush with hot water, then work a set of drain rods through the gully, turning clockwise only. Most surface blockages of leaves, silt and food waste clear this way. If two rodding attempts fail, or sewage is backing up, stop: the blockage is deeper or compacted, and forcing it usually makes the professional job bigger.
A blocked drain outside the house is one of the few drainage problems a homeowner can genuinely have a go at fixing. Plenty of gully blockages are nothing more than leaves, silt and kitchen fat sitting just below the grate, and ten minutes with gloves and a bucket sorts them. This guide walks you through the honest DIY method, step by step, then tells you plainly where the sensible stopping point is, because the difference between a cheap fix and an expensive one is often just knowing when to put the rods down.
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Before you start: work out which drain it is
Not every blocked drain outside your house is yours to fix, or yours to pay for. In England, you are generally responsible for the drains that serve only your property and sit inside your boundary. Once the pipe crosses your boundary, or joins a run shared with a neighbour, it usually becomes a lateral drain or public sewer, and those belong to the water company. Across Cornwall and Devon that is South West Water, and they clear blockages in their own pipework free of charge.
The quick test: if your neighbours have gurgling plugholes or standing water at the same time as you, the blockage is probably in a shared or public section, so report it to South West Water before you spend a penny. If only your property is affected, and the gully or chamber on your land is the one holding water, it is very likely yours. We cover the full picture in our guide to who is responsible for a blocked drain.
How to unblock an outside drain, step by step
Step 1: Kit up properly
You want long rubber gloves, old clothes, eye protection if you have it, a bucket, and something to kneel on. Outside drains carry foul water as well as rainwater, so treat everything that comes out of one as contaminated. Wash thoroughly afterwards, and keep cuts covered.
Step 2: Lift the grate or cover
Most outside blockages sit in the gully, the trapped pot under the grate where your kitchen waste, gutter downpipes or patio drainage enter the system. Lever the grate up with a flat screwdriver if it is stuck. If the problem is further along the run, find the nearest inspection chamber cover and lift that instead, using proper lifting keys or a spade edge, never your fingers under the rim.
Step 3: Clear what you can reach by hand
This is the unglamorous step that clears more gullies than any gadget. Scoop out the leaves, silt, grease and debris sitting in the gully pot and drop it in your bucket. Keep going until you can feel the outlet where water leaves the pot. A surprising number of "blocked drains" are simply a full gully trap, and once it is emptied the water runs away on its own.
Step 4: Flush with hot water
Pour a couple of buckets of hot (not boiling) water into the gully. If the standing water drops away, run a tap or hose for a few minutes to confirm the flow is properly restored, then put the grate back and you are done. Boiling water is best avoided on older ceramic pots and plastic fittings, which can crack with sudden heat.
Step 5: Rod the drain
If water still stands, it is time for drain rods, which cost little from any DIY shed. Screw two or three sections together with the plunger head fitted, feed them into the outlet, and work them forward with a firm push and pull. Add sections as you go. The one rule that matters: only ever twist the rods clockwise. Turn them anticlockwise and the sections unscrew, leaving a rod stuck in the pipe, which turns a blockage into an excavation.
Step 6: Flush again and watch the flow
When you feel the blockage give, flush the run through with several buckets of water or a hose. Watch the gully for a good five minutes. Fast, steady flow with no gurgling means you have cleared it. Slow drainage, or water that backs up again within days, means you have poked a hole through the blockage rather than removed it, and that is your cue to read the next section.
What works and what does not
| Method | Good for | Honest verdict |
|---|---|---|
| Gloved hand and bucket | Full gully traps, leaves, surface debris | The best first move. Clears most gully blockages on its own. |
| Hot water flush | Soft fat and soap build up near the surface | Cheap and useful after hand clearing. Avoid boiling water on old pots. |
| Drain rods | Blockages within a few metres of the access point | Effective on soft blockages. Clockwise turns only. |
| Soda crystals or washing up liquid | Greasy gullies, as prevention | Fine as maintenance, rarely clears an established blockage. |
| Caustic soda and chemical unblockers | Very little outdoors | Avoid. Ineffective on silt and roots, hazardous to whoever rods the drain next, hard on old pipework. |
| Pressure washer down the gully | Nothing, honestly | Not a substitute for jetting. It lacks the flow and the right nozzle, and can force debris into a worse position. |
The mistakes that make a blockage worse
Three DIY habits reliably turn a modest call out into a bigger one. The first is over-rodding a compacted blockage: repeated forcing can pack fat and wipes into a dense plug, or shove the mass further along the pipe to somewhere with no access. The second is the anticlockwise twist that unscrews a rod inside the run. The third is pouring chemicals into a drain that then does not clear, leaving standing caustic water that has to be dealt with before anyone can work safely.
None of this is said to put you off. Clearing a gully by hand and rodding a soft blockage are genuinely sensible jobs to do yourself. The skill is recognising the blockage that is not going to give, early, before effort turns into damage.
When to stop and call a professional
Stop the DIY and pick up the phone if any of these apply:
- Two rodding attempts have not cleared it. The blockage is deeper, compacted, or past a bend your rods cannot work through.
- Sewage or grey water is backing up into the house, or overflowing from a gully or chamber. That is a health hazard, not a weekend job.
- The same drain keeps blocking. A recurring blockage nearly always has an underlying cause: roots, a cracked or dropped pipe, or heavy scale. Our guide to why drains keep blocking explains the usual suspects.
- You cannot find an access point, or the blockage sits under a building or driveway.
- There is a smell of foul water that will not go, even when the drain seems to run.
What a professional brings is not just stronger arms. High pressure drain jetting cuts through compacted fat, silt and root ingress and flushes the whole bore of the pipe clean, which is why a jetted drain stays clear where a rodded one often reblocks within weeks. For a straightforward stubborn blockage, a professional drain unblocking visit is usually quick, and a good local firm will give you a fixed price on the phone before anyone travels. Typical UK costs are covered honestly in our drain unblocking cost guide.
Around Plymouth, south east Cornwall and south and west Devon, that local firm can be us. We will also tell you, free of charge, if the blockage looks like South West Water's responsibility rather than yours.
Frequently asked questions
What is the best way to unblock an outside drain?
Start by lifting the grate and clearing what you can reach by hand, wearing gloves. Then flush the gully with a bucket of hot water. If the water still stands, use a set of drain rods with a plunger head, turning them clockwise only so the sections do not unscrew inside the pipe. If two rodding attempts do not clear it, the blockage is likely deeper or compacted, and professional jetting is the sensible next step.
Can I use caustic soda or chemical unblockers on an outside drain?
We advise against it. Chemical unblockers rarely shift the fat, silt and root material that blocks outside drains, and a gully full of caustic solution becomes a hazard for whoever works on the drain next, including you. They can also damage older pipework. Mechanical clearing with rods or high pressure jetting is safer and far more effective.
Why does my outside drain keep blocking after I clear it?
A drain that reblocks in the same spot almost always has an underlying cause, such as a cracked or dropped pipe, tree roots, heavy scale, or a build up of compacted fat that rodding only pokes a hole through. A CCTV drain survey shows what is happening inside the run so the cause can be fixed once, rather than the symptom cleared repeatedly.
Who is responsible if the blocked drain is outside my boundary?
In England, drains serving only your property within your boundary are your responsibility. Shared drains and pipes beyond your boundary are usually lateral drains or public sewers, which belong to the water company. In Cornwall and Devon that is South West Water, and if the blockage is in their pipework they will normally clear it free of charge.
Rods not shifting it? We will
We clear stubborn outside drains across Plymouth, south east Cornwall and south and west Devon with high pressure jetting, at a fixed price agreed before we set off. Tell us what you have tried and we will tell you honestly what it needs.
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