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The first triage question isn't "how do I clear it" — it's "where is it?" One fixture, the whole house, or the street: three different problems, three different answers.
Quick triage: one slow sink is a local clog you can probably tackle; every fixture backing up at once is the main drain; sewage rising at an outside manhole — or your neighbours suffering too — may be NI Water's sewer, not yours. Unsure which you've got? Ring 020 4577 2888 and describe it — any hour.
Run the taps and read the map. A single slow fixture is local; several at once means the blockage is downstream where their pipes meet.
Triage a drain the way you'd triage anything: establish the extent before you treat. A bathroom basin gurgling on its own points to hair and soap in its own trap — thirty centimetres of pipe, not a catastrophe. The kitchen sink alone usually means fat and food waste in the local run.
But when the downstairs loo backs up as the bath empties, or an outside gully overflows whenever the washing machine drains, the blockage sits in the shared pipework — and plunging one fixture is treating the symptom furthest from the disease. That's the point at which a plumber with rods or a jetting rig stops being a luxury and starts being the cheap option, because a main-drain blockage left to ripen eventually comes back up through the lowest fixture in the house.
Boiling water, a plunger, a hand auger, and a trap you unscrew yourself — in that order. Escalate calmly; stop when force is the only idea left.
What doesn't belong on the list: dismantling anything beyond the trap, poking with improvised wire (it scratches pipe and snags), or a second and third dose of caustic cleaner into standing water — see the FAQ below for why that one bites the person who comes after you.
Fat, wipes and "flushable" anything — the holy trinity of blocked drains. Prevention is a jar by the cooker and a bin by the loo.
Cooking fat goes down as liquid and sets in the pipe as candle wax — every fried breakfast quietly narrowing the bore. Wipes labelled flushable will indeed flush; they just won't break down, and somewhere down the line they knit together with the fat into the dense mats that drainage engineers pull out by the metre.
The house rules that keep this page theoretical: fat into a jar or tin, wipes and cotton buds and dental floss into the bin, a hair catcher on the shower plughole, and a monthly very-hot-water rinse through the kitchen run. In an older terrace where your drain may share history — and pipework quirks — with the house next door, those habits protect more than one household.
Your drains inside the boundary: yours. The public sewer, and generally shared sewers: NI Water's. Neighbours affected too? Report before you pay anyone.
The boundary rule does a lot of work here. Pipework serving only your property, inside your boundary, is the householder's to maintain. Once drains join with a neighbour's or cross into the street, you're generally into public-sewer territory — NI Water's responsibility across the north, Derry included.
The tell-tale signs the problem is bigger than your house: more than one property backing up at once, a manhole in the street lifting or overflowing, or gullies along the road all sitting full. In that case report it to NI Water first — paying privately to clear a public blockage helps nobody. If it's genuinely unclear which side of the line the trouble sits on, that's a fair question to put to the plumber on the phone before anyone lifts a cover.
Use caution rather than enthusiasm. Caustic products can be harsh on older pipework, dangerous if they splash back, and a genuine hazard for whoever puts a plunger or rods into the water afterwards. If you do try one, follow the label exactly, never mix products, and always tell the plumber what went down before they start work.
Stop flushing — a second flush on a full pan is how floors get flooded. Let the level drop if it will, then try a toilet plunger or a bucket of water poured steadily from waist height to push the blockage through. If it won't shift after a couple of calm attempts, ring rather than force it.
A smell with free-running water often means a drying trap, a partial build-up coating the pipe, or a venting issue rather than a hard blockage. Running water through seldom-used fixtures weekly can cure a dried trap. A persistent smell with slow drainage, though, is a blockage forming — cheaper to deal with early.
Broadly, drains inside your boundary serving only your property are yours; the public sewer beyond, and shared sewers, are generally NI Water's territory. If neighbours are backing up at the same time as you, or a manhole in the street is overflowing, report it to NI Water before paying anyone — a plumber can help you tell which side it's on.
The main page — the triage board and the areas this line covers.
Go to home →The sixty-second triage for escaping water.
Read the guide →Pressure drops, no heat, error codes — and the gas rule.
Read the guide →No invented prices — how charging works and what to ask first.
Read the guide →Pressure, timer, tripped switch, diverter valve — the checks before the call.
Read the guide →Prevention that costs pennies, thawing that doesn't end in a flood.
Read the guide →The signs, the stopcock test, and when a damp patch turns urgent.
Read the guide →Ring any hour to be connected with a local plumber covering Derry and the villages around it — and say what you've already tried.
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