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Published by Mo's Plumbing and Heating
What Is Foul Water Drainage?
Foul drainage carries everything that leaves the inside of your building: toilets, basins, baths, showers, the kitchen sink and the washing machine. The part most people want to know is not what it is but where their responsibility for it ends, because that determines who pays when something goes wrong out in the street.
The Short Answer
Foul water is waste from inside the property, and it goes to treatment rather than to a watercourse. Everything from the fittings joins a soil stack or a branch, leaves the building, and runs to the public sewer. Your responsibility covers the drains within your property boundary; beyond that boundary the pipework is generally the water authority's, and in a shared building the pipework serving several properties is usually common rather than yours alone.
What Counts as Foul
Broader than people assume, and the boundary is about where the water has been rather than how dirty it looks.
Obviously foul: anything from a toilet. Less obviously but equally: basins, baths and showers, the kitchen sink, dishwashers and washing machines. All of that is waste water from inside the building and all of it goes to treatment.
Kitchen waste in particular gets treated as though it were less serious than it is, because the water looks clean going in. It carries fats, oils and food solids, and those are what build up in drains and, at scale, in sewers.
Not foul: rainwater off a roof or a hard surface, and ground water. Those belong to the surface water system, which is a separate network with separate rules, set out on its own page.
The practical consequence of the distinction is that the two must not be cross-connected, in either direction, which is covered in more detail on the surface water page.
Yours, Theirs, or the Building's
The question behind most searches for this, and the answer has a general shape with genuine local variation.
Broadly, the pipework inside your property boundary that serves only your property is yours to maintain and repair. That includes the branches from your fittings, the soil stack where it serves you alone, and the runs and inspection chambers within your ground.
Beyond the boundary, and for the sewer that collects from multiple properties, responsibility generally sits with the water authority rather than with individual householders. That transfer of responsibility is why a blockage in the street is a different conversation from a blockage in your garden.
In a flatted building there is a middle category that catches people out: pipework serving several flats is common rather than belonging to whichever household noticed the problem. The soil stack running up the back of a tenement serves every flat on that stack, so a blockage in it is a building matter.
The exact boundaries and what falls to whom vary, and it is worth establishing rather than assuming when a repair is being discussed. If your building is factored, the factor holds the paperwork on what is common. Scottish Water is the authority for public sewers here, and for anything in the street or beyond the boundary they are the right first call rather than a private contractor.
What Should Never Go Down It
The short version is nothing but the obvious, and the longer version is worth having because the reasons differ.
Wet wipes, of any description, including those marked flushable. That word describes leaving the pan rather than reaching the sewer. They do not break down, they knit together, and they are comfortably the most common thing found in blocked drains.
Sanitary products, nappies and cotton buds. Same problem: they pass the pan and then catch on everything downstream.
Cooking fat and oil, which is the kitchen equivalent. It leaves the sink as a liquid and sets solid as it cools in the pipe, gradually narrowing the run until something else catches on it. Into a container and the bin rather than down the sink.
Coffee grounds, which behave like fine sand and settle in low points.
And during building work, sand, plaster and cement, which set hard in a trap. That is worth mentioning to anybody working in the property, because it is done thoughtlessly rather than deliberately.
How It Is Built
Useful to know because it explains why blockages happen where they do.
Each fitting has a trap, the bend holding a plug of water that stops sewer gas coming back into the room. Every basin, bath, sink and toilet has one, and a dry trap on a rarely used fitting is the usual explanation for a smell.
Branches run from the fittings to a soil stack, which is the vertical pipe carrying everything down. The stack is also vented, usually to a terminal above the roofline, which lets air in and out so that a flush somewhere does not siphon the water out of somebody else's trap.
At the bottom the stack turns and runs underground, through one or more inspection chambers, to the sewer connection. The chambers exist so the run can be inspected and rodded, which is why finding them matters when there is a blockage.
The vent is worth knowing about because when it is blocked, the symptoms look like a drainage fault of a different kind: gurgling fittings, traps emptying themselves, and smells appearing in rooms with no obvious cause.
Signs Something Is Wrong
What to look for, roughly in order of how much it matters.
Slow drainage at one fitting is a local blockage in that branch. Slow drainage at several at once is further along in the shared run.
Gurgling from a basin or bath when a toilet is flushed means air is being pulled through a trap it should not be, which points at a partial blockage or a vent problem downstream.
Smells indoors with no visible cause usually mean a dry trap or a broken seal rather than a blockage. Pouring water into rarely used fittings is worth trying before anything else.
Waste appearing in the lowest fittings in a building, or backing up at ground level, is the serious one. That means the blockage is downstream of everything and it needs attention rather than plunging.
And a drain that blocks repeatedly in the same place is telling you about the pipe rather than about what went down it, which is a survey question rather than another clearance.
One Stack, Eight Households
The reason responsibility is a live question in this city rather than an academic one is that most of the housing is flatted, and flatted buildings share the pipework that matters most.
A traditional tenement has a single soil stack serving the same room in every flat up the close, so eight kitchens or eight bathrooms can be connected to one vertical pipe. Everything above you passes your branch on the way down. That means a blockage low in the stack shows up as waste backing into the lowest fittings in the building, which is why the ground floor flat frequently discovers a problem that originated three floors up, and why the household that notices is very often not the household that caused it.
It also means the repair is usually a building matter rather than an individual one. Common pipework is a factor conversation, and establishing that early matters, because otherwise one household arranges and pays for work on a pipe that eight households use. The five minutes spent knocking on a door to ask whether anyone else is affected is the most valuable five minutes available at the start of one of these.
The other Glasgow specific is access. Inspection chambers in back courts have frequently been built over during the decades since they were laid, and finding the cover under decking, a bin store or a slab is regularly the longest part of the job. Knowing where yours is before you need it is worth doing on a dry afternoon.
Beyond the property boundary, Scottish Water is responsible for the public sewer, and for anything in the street that is the right first call rather than a private contractor.
When to Call Someone Out
Call when more than one fitting is affected, when waste is backing up into the lowest fittings in the building, or when the same drain blocks repeatedly, which is a defect in the pipe rather than a clearance question. Before that, it is worth establishing whether neighbours are affected, because a problem in common pipework is a building matter and that changes both who arranges the work and who pays for it. Paul leads the drain team and Kyle runs the high pressure jetting. If the problem is clearly beyond your boundary or in the street, Scottish Water is the right first call rather than us.
Drain Repairs in GlasgowCommon Questions
Yes, and so does the dishwasher, the bath and the kitchen sink. The test is where the water has been, not how dirty it looks going in. Kitchen waste in particular gets treated as though it were clean because it looks it, and the fats and food solids in it are exactly what builds up in drains further along.
What Locals Say About Mo
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“Our radiator pipe was bent and leaking. They answered straight away… Guy was here an hour later and he was wearing ID, very professional, patient and kind. We just got a new carpet in this room and he done an amazing job on getting little to no water on it. Couldn't recommend enough, price was reasonable.”
Kayleigh A. · Glasgow
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“We lost heating just in time for the coldest day of the year with a baby in the house… When I contacted them they were ready to dispatch that night. Fixed by the afternoon. Quoted that morning and no extra charges were added. Honestly cannot thank them enough.”
Jemma M. · Glasgow
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“As a small business owner, I needed a drainage company that could respond quickly. The team attended first thing in the morning, cleared the blocked drain and carried out a full CCTV survey. All documentation emailed across promptly. Professional, efficient and great value for money.”
Eric V. · Glasgow
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Read Next
Full guide
What Is a French Drain?
A trench, a perforated pipe at the bottom, a permeable membrane lining it, and clean stone filling the rest.
What Is Surface Water Drainage?
Surface water drainage takes rainwater from roofs and hard surfaces to a surface water sewer, a soakaway or a watercourse.
What Is a French Drain?
A trench, a perforated pipe at the bottom, a permeable membrane lining it, and clean stone filling the rest.
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