Blocked Drains: Toilets, Sinks and Kitchen Pipes

Most blocked drains are local, simple and fixed with a plunger and ten minutes of mild unpleasantness. A smaller number sit further down the line, where no amount of plunging helps and some of it makes things worse. The useful skill is telling the two apart quickly, before you've flooded the bathroom floor.

How the drains in a home fit together

Follow the water from the plughole.

• The trap. Under every sink, bath, shower and toilet is a bend that holds water. That water seal stops sewer smells coming back into the room. It is also where hair, soap, grease and lost earrings collect. Under a basin it may be a U-shaped trap or a compact bottle trap; in a toilet it is moulded into the pan.
• The branch. From the trap, a waste pipe runs to the main vertical pipe. Basin, bath and sink wastes are typically 32–40 mm plastic pipe; toilets use pipe of around 100–110 mm.
• The stack. The soil and vent stack is the large vertical pipe, inside or outside the building, that carries everything down. Its top is open above the roof or fitted with an air admittance valve, so water can fall without sucking the traps dry.
• The gully. Outside, kitchen waste and rainwater often discharge into a gully: a trapped drain under a grid at ground level.
• The inspection chamber. Underground pipes meet at chambers with lift-off covers, often called manholes. These are the access points for rods and cameras.
• The sewer or private system. Finally everything joins the public sewer, or a septic tank or treatment plant in many rural homes.

In blocks of flats, several homes share each stack and the drains below ground, which matters a great deal when something goes wrong.

Local blockage or main drain?

Let the house tell you where the problem is.

• One fixture slow, everything else fine. The blockage is in that trap or its branch. Start there.
• Basin and bath in the same room both slow, toilet fine. Probably the shared branch before it joins the stack.
• The toilet gurgles or its water level rises when the bath or washing machine empties. The problem is lower down, in the stack or the underground drain.
• Water comes back up in the lowest fixture, often a ground-floor shower or toilet, when someone upstairs uses water. Main drain, almost certainly.
• The outside gully overflows or an inspection chamber is full. Main drain. Lift the cover (they are heavy, so lift with your legs and wear gloves). If this chamber is full and the next one downstream is empty, the blockage sits between them.

If more than one home in your building is affected, stop and tell the building manager. That is a shared drain, and not one to start rodding on your own.

The tool kit

Add rubber gloves, safety glasses, an old towel and a bucket. Most bathroom blockages are hair and soap scum caught in the trap, so unscrewing the trap over a bucket often beats any tool; our guide to unblocking a bathroom sink shows how. Toilets have their own technique and their own hazards, covered step by step in how to unblock a toilet.

Chemical drain cleaners

Shop-bought drain cleaners fall into three broad groups. Caustic products based on sodium hydroxide turn grease into a soapy mass. Acid cleaners, usually sulphuric acid, are stronger and more dangerous. Enzyme and bacterial products work slowly and suit regular maintenance better than clearing a full blockage.

The problem with the strong ones is that they have to reach the blockage to work. In a drain that has stopped completely, they sit in the trap: a pool of corrosive liquid waiting for whoever arrives next with a plunger. They can also damage old metal pipes, attack some seals and upset septic tanks.

What not to do: never mix two drain products, or a drain product with bleach, because some combinations give off toxic gas or react violently. Never plunge or rod a drain with chemical cleaner sitting in it. Never pour boiling water into a toilet pan or down plastic waste pipes, as it can crack porcelain and soften joints. And if you've already used a chemical, tell whoever comes to clear the drain.

Prevention, room by room

Kitchen

Fat is the main culprit. Cooking oil and grease are liquid in the pan and set solid in a cold pipe, picking up food scraps and coffee grounds as they go. Wipe greasy pans with kitchen paper before washing them, pour used oil into a jar for the bin, and fit a strainer in the plughole. We list the other usual offenders, from rice to eggshells, in what blocks a kitchen drain.

Bathroom

• Fit a hair catcher in the shower and bath wastes.
• Pull out the basin's pop-up plug every few weeks and clean the gunk off it.
• Flush only toilet paper and what the body produces. Wet wipes, including ones labelled flushable, cotton buds, dental floss and sanitary products all go in a bin.

Utility room and outside

Washing machines shed lint and the odd sock; a lint catcher on the end of the waste hose helps. Outside, clear leaves off gully grids in autumn, and remember that trees near old clay drains can push roots into the joints.

Who is responsible for shared drains

There is no single answer. Who owns and maintains a drain depends on the country, local law and the type of building. In some places, a pipe serving one property belongs to the owner up to the boundary or the public sewer, while pipes serving several properties belong to the water or sewerage company. In others, neighbours share the cost of a common drain. In apartment buildings, the stacks and below-ground drains are usually common parts, maintained through the management company, owners' association or landlord.

Tenants should report blockages to the landlord rather than hiring someone directly, unless the tenancy says otherwise. And if you're unsure who owns a pipe, ask the water company, building management or landlord before paying for work on it.

When to call drainage professionals

Bring in a drainage specialist when:

• the blockage is in the main drain or affects more than one home;
• a drain blocks again within weeks of being cleared;
• sewage appears in the garden or comes up through a floor drain;
• you suspect roots, a collapsed pipe or a section that has sunk;
• you're buying an older property and want to know the state of its drains.

Two tools do most of the work. A CCTV drain survey pushes a waterproof camera along the pipe to show cracks, root intrusion, displaced joints and fat build-up, with a recording and a written report. A high-pressure jetter sends a hose with a rotating nozzle through the pipe, cutting through grease and debris that rods only shove along. Ask to see the camera footage, ideally before and after jetting, so you know the blockage was cleared rather than moved. If the survey shows structural damage, repairs range from patch lining to replacing a length of pipe.

Quick answers

Why does my drain smell when it isn't blocked?

Usually a dried-out trap. Basins, showers and floor drains that are rarely used lose their water seal to evaporation, letting sewer air through. Run the tap for a minute to refill it. If the smell persists, a loose trap joint or a venting fault is the next suspect.

Are flushable wipes safe to flush?

Treat them as unsafe. Many break down far more slowly than toilet paper and combine with fat in drains and sewers to form solid blockages.

How can I tell if roots are getting into the drain?

Slow drainage that keeps returning, gurgling at the outside gully and trees within a few metres of the drain run are the clues. A CCTV survey confirms it; rods alone won't tell you.