Most household blockages are caused by fat, wipes and food waste building up in one fitting's pipework, and a plunger plus a trap clean-out will often shift them. If several fixtures back up at once, or waste surfaces at an outside gully, the problem is in the main drain — and if that drain is a shared public sewer, in Northern Ireland it is NI Water's responsibility rather than yours.
What causes the blockage in the first place
Drains rarely block without help. Warm cooking fat poured down the sink sets like candle wax as it cools, and every wipe, cotton pad and scrap of food that follows sticks to it. So-called flushable wipes are the drain trade's most reliable source of work: unlike toilet paper they don't break down, and they knit into stubborn plugs. The saving habit is simple — cooled fats into a jar or the bin, wipes and sanitary products in the bin every time, a strainer over the plughole.
Age plays its part too. The Victorian and Edwardian terraces near Ballymena town centre often still drain through original clay runs and cast iron stacks, where decades of scale give debris something to snag on. An old drain isn't doomed; it just forgives bad habits less readily than a modern plastic run in a new build at Galgorm.
Clearing a simple blockage
Start small and work up. Clear what you can see at the plughole, then plunge — with a damp cloth over the overflow so the pressure goes down the pipe rather than back at you. Hot (not boiling) water with washing-up liquid helps break down grease. Under most sinks the trap unscrews by hand: bucket beneath, open it up, and the culprit is often sitting right there. Avoid the strongest chemical cleaner on the shelf — caustic products sit in a blocked pipe as a hazard for whoever opens it next, and they're unkind to older pipework.
If one fixture still won't drain, the blockage has moved beyond arm's reach and a plumber's tools — rods, an auger, sometimes a jetting rig — earn their keep.
Signs the problem is in the main drain
A single slow sink is a local problem. A toilet that rises when the bath empties, gurgles from several plugholes at once, or waste appearing at an outside gully or manhole tell a different story: the main drain is obstructed and everything upstream is backing up together. In rural properties around Portglenone or Kells, a struggling septic tank or soakaway can produce the same symptoms and is worth ruling out. Main-drain work is not a plunger job — it needs access, rods or jetting, often a camera.
Who is responsible for the drain
Ownership follows the pipe. Drains serving only your property, within your boundary, are generally the owner's to maintain and unblock. Once the pipework becomes a public sewer — including shared sections carrying more than one property's waste as part of the public network — responsibility in Northern Ireland passes to NI Water. That distinction matters before you spend money: if a shared sewer under the street is the true culprit, it isn't a private repair at all. A plumber or drainage specialist can help establish where your drain ends and the public sewer begins.
Common questions about blocked drains
What should I never pour down the drain?
Cooking fats, oils and grease are the big one — they set hard in cold pipes. Wet wipes, even ones labelled flushable, along with kitchen roll, cotton wool, sanitary products and food scraps all belong in the bin, not the drain. Coffee grounds and plaster are quiet offenders too.
How do I unblock a sink myself?
Start by clearing the plughole and trap of debris, then try a plunger with the overflow blocked by a damp cloth. Hot (not boiling) water with washing-up liquid can shift greasy build-up. If the trap under the sink is accessible, unscrew it over a bucket and clean it out. If none of that works, the blockage is likely further along the pipe.
How do I know if the blockage is in the main drain?
If more than one fixture is affected at once — the toilet backing up when the bath empties, gurgling from several plugholes, or waste appearing at an outside gully or manhole — the problem is almost certainly in the main drain rather than a single fitting's pipework.
Who is responsible for a blocked sewer in Northern Ireland?
As a general rule, drains serving only your property are the owner's responsibility, while public sewers — including sections shared between properties that form part of the public network — are the responsibility of NI Water. A plumber or drainage specialist can help establish where your drain ends and the public sewer begins.
More help
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