How to unblock a drain, and how to tell when it's a sewer problem

How to unblock a drain, step by step

The quickest way to unblock a drain is to work from the top down: find out which drain is blocked, then try the gentlest fix first and stop when the water runs freely. Redland City Council says that if only one sink or toilet is draining slowly or blocked while everything else works fine, the problem is most likely in your home's plumbing (Redland City Council).

1. Check the other taps, showers and toilets. One slow fixture is a local blockage. Several at once is a drain problem.
2. Pull hair and gunk out of the plughole or strainer by hand, wearing gloves.
3. Run hot water from the tap, not a kettle, for a minute or two.
4. Use a plunger with the overflow hole covered by a wet cloth.
5. Clean the trap under the sink or basin if it unscrews by hand.
6. Feed a hand drain snake into the fixture waste.

If none of those steps works, or the problem shows up in more than one place, the blockage is further down the house drain, and that is a job for a licensed plumber.

Which drain is blocked? Start with the symptoms

You can tell which drain is blocked by what you notice and where you notice it. A slow basin points to the basin. Gurgling in several rooms points to the drain those rooms share. Water spilling from the overflow relief gully (ORG), the grated drain in the ground outside, points further down again. Use the table below to match what you see to the likely spot and the right next step.

For a toilet that won't clear, read what to do about a blocked toilet.

Signs the blockage is in your sewer line, not one fixture

A blockage is in your sewer line, rather than one fixture, when the problem shows up in more than one place or outside the house. The clearest sign is the overflow relief gully. Redland City Council describes the ORG as a drain-like feature that directs sewage outside your house if there's a blockage or if the sewer system becomes overloaded during storms (Redland City Council). Logan City Council adds that the ORG grate should pop off to release the pressure from the pipes (Logan City Council).

• The shower drain fills when you flush the toilet.
• Water rises in the floor waste when the washing machine empties.
• Two or more fixtures are slow at the same time.
• The ORG grate has lifted, or the ground around it is wet with grey water.

Timing tells you which side of the fence the blockage is on. Redland City Council says that if the ORG overflows whenever you are using water in the house, there may be a blockage in your wastewater line and you should contact a plumber (Redland City Council, ORG guidance). If the ORG overflows when no water is being used at the property, the blockage is likely to be in the council's sewer main (Redland City Council).

What a gurgling drain is telling you

A gurgling drain is telling you that air is being pushed back up the pipes, and what that means depends on the weather. During heavy rain, Redland City Council says you may notice gurgling toilets or slow-flowing drains because the sewerage network becomes temporarily overloaded, and the gurgling will resolve on its own as levels return to normal (Redland City Council).

The council also says a gurgling toilet usually means the ORG is doing its job and preventing discharge occurring inside your house, and that calling a plumber isn't necessary unless there is an actual blockage within your property's wastewater line (Redland City Council, ORG guidance).

Gurgling in dry weather is a different story. If a basin gurgles every time the bath empties, or every drain in the house gurgles when the toilet flushes, it can mean water is struggling to get past a partial blockage in the shared house drain. Gurgling plus a bad smell often has its own cause, covered in the guide to smelly drains and sewer flies. Dry-weather gurgling across the house is a reason to call a plumber before the drain stops completely.

Safe DIY methods, in the order to try them

The safe DIY methods for a blocked sink, shower or basin are mechanical: lift the blockage out, push it through or pull it back. Stop as soon as the water drains freely.

1. Clear the plughole. Lift out the strainer or plug and pull out hair and scraps with gloved fingers.
2. Run hot tap water to soften soap and light grease. Use the tap, not a kettle (see below).
3. Plunge. Fill the basin a few centimetres so the plunger cup is covered, block the overflow hole with a wet cloth, and pump firmly a dozen times.
4. Clean the trap. Put a bucket underneath, unscrew the bottle trap or U-bend under the sink or basin by hand, empty and rinse it, then refit it hand tight and check for drips.
5. Use a hand drain snake. Feed a hand-held snake down the plughole or the open trap arm, turn the handle as you go, and pull back slowly to bring the blockage out.

A plug of fat, wipes or hair needs to be broken up or pulled out, so go straight to the mechanical steps above.

What not to put down a blocked drain

Don't put caustic or acid drain cleaners, mixed products or a kettle of boiling water down a blocked drain. Caustic and acid cleaners can be dangerous, mixed products can release toxic gas, and one PVC pipe maker advises avoiding full-bore and extended hot discharges, so none of these is the right first step.

• Caustic and acid cleaners. Product Safety Australia warns that caustic soda-based cleaners contain chemicals and poisons that can be dangerous (ACCC Product Safety). One gel drain cleaner sold here carries the label warning that it is a corrosive product (Selleys). Safe Work Australia notes that corrosives damage the skin and eyes on contact. If the drain doesn't clear, that chemical is now sitting in the water you have to plunge or bail.
• Mixing products. Safe Work Australia says corrosive chemicals are often incompatible with each other, and gives the example that chlorine coming into contact with acid releases poisonous chlorine gas (Safe Work Australia). Never add a second cleaner, or bleach, on top of a first.
• Boiling water in plastic pipes. If your waste pipes are plastic PVC, take care with heat. One Australian fittings maker gives PVC-U drainage fittings a softening point of about 80°C and a recommended maximum continuous operating temperature of 60°C, while noting that the pipes can cope with typical discharges at higher temperatures but full-bore and extended periods of discharge should be avoided (Holman Industries). A blocked drain holds water in the pipe rather than letting it run away, so hot tap water is the gentler choice.

Why drains block in south-east Queensland homes

Common causes of blockages and overflows in south-east Queensland homes include tree roots, defects from ground movement, fats and wipes, and stormwater overloading the sewer network. Redland City Council lists tree roots entering and growing inside pipework among the common causes of blockages and overflows (Redland City Council).

Roots usually get in through damage. An Urban Utilities information form (2010) says the majority of chokages are caused by some defect that has developed in the drain, generally through pressure from ground movement, and that cracked or broken pipes most commonly allow tree roots in. The same form says that type of choke will recur unless the defective section of drain is repaired (Urban Utilities). The tree roots and pipe relining guide covers the repair options.

Kitchen and bathroom habits matter too. Logan City Council says fats, oils and food scraps quickly solidify, sticking to the walls of pipes (Logan City Council), and lists wet wipes (including 'flushable'), tissues, paper towels, rags, sanitary items and cotton buds as things that may block your pipes (Logan City Council).

Storms add another load. Redland City Council says stormwater must not be directed into the sewer system under any circumstances (Redland City Council), and that illegal stormwater connections to the sewer, such as roof or yard drainage, contribute to network overloading during heavy rain (Redland City Council).

Your drain or the utility's? Who fixes what in Brisbane, the Redlands and Logan

The pipes on your side of the sewer connection are yours to maintain, and faults in the sewer main are the water utility's responsibility to fix.

Urban Utilities says it maintains and operates the sewerage service from the property connection point for your property (Urban Utilities customer charter). Redland City Council says that if a sewer blockage occurs within your property, you must first engage a plumber to confirm the blockage is not on your side. If the inspection opening is dry when a tap runs inside, there may be a blockage in your plumbing. If it is holding liquid or overflowing, there may be a blockage in the council's main (Redland City Council). Logan City Council repairs blocked and damaged sewerage mains outside of your property boundary (Logan City Council), and asks you to call 07 3412 3412, 24 hours a day, if your plumber finds the blockage is in its network (Logan City Council).

When to stop and call a licensed plumber, and what they'll do

Call a licensed plumber once the problem is beyond one fixture you can reach. The drainage work the Queensland Government says you can do yourself, or have an unlicensed person do, includes cleaning or maintaining ground-level grates to traps on sanitary drains and replacing caps to ground-level inspection openings on sanitary drains (Queensland Government). You can check a plumber's licence online or by calling the QBCC on 139 333.

Redland City Council suggests making sure the plumber has jet rodding and a pipe inspection camera (CCTV) to do the job (Redland City Council). Jim Monger Plumbing and Gas offers jet rodder and electric eel drain clearing backed by CCTV inspections, under QBCC licence 15504687. See blocked drain clearing in Brisbane, or the local pages for Capalaba and Victoria Point.

What affects the size of the job: where the blockage is and what caused it, how easy the drain is to get to, whether a camera inspection is needed to find the cause, and whether the camera shows roots or a broken pipe that needs repair rather than just clearing. For an overflow after hours, call 0418 871 269 or see emergency plumbing.

Keeping drains clear: simple habits that prevent the next blockage

Many drain blockages can be prevented by what you keep out of the pipes, and keeping the overflow relief gully clear lets it do its job. Logan City Council's rule for toilets is simple: only pee, poo and toilet paper should go down the loo (Logan City Council).

• Bin wet wipes, even the ones labelled flushable. Logan City Council says to wrap them and put them in the garbage bin.
• Wipe greasy pans with paper towel before washing, and put cooled fat and oil in a sealed container for the bin.
• Use a sink strainer in the kitchen and a hair catcher in the shower.
• Keep the ORG grate loose and clear. Redland City Council says it should not be covered by pot plants, tiling, paving or landscaping, and roofwater pipes should not feed directly into it (Redland City Council, ORG guidance).
• Think about where the drain runs before planting trees, so roots have less chance to find a cracked joint.

If one drain keeps blocking even with good habits, a camera inspection shows whether a root, a sag or a damaged pipe is catching debris.