If you’re dealing with a blocked drain, you’re not alone — blocked drains are one of the most common plumbing issues we attend across Sydney. Understanding what caused the blockage is the first step toward fixing it properly and preventing it from happening again. Below are the most common causes of blocked drains we encounter, what happens inside your pipes when they occur, and how a professional plumber resolves each one.
Across thousands of Sydney call-outs, these eight causes account for almost every blocked drain we see. For each one, here’s what’s happening inside your pipes — and how a professional plumber resolves it.
Cause 1 of 8
1
Tree roots are the number one cause of blocked sewer drains in Sydney, particularly in older suburbs across the Eastern Suburbs, Inner West, and North Shore where mature trees line streets and properties.
What Happens
Tree roots are naturally attracted to the moisture and nutrients inside drainage pipes. They enter through hairline cracks, loose joints, and connection points — especially in ageing clay and earthenware pipes common across Sydney’s older housing stock. Once inside, roots expand rapidly, forming dense masses that trap waste and eventually block the pipe entirely.
How We Fix It
Our plumbers start with a CCTV drain camera inspection to locate exactly where roots have entered and assess severity. For active root blockages, we use high-pressure hydro-jetting combined with root cutting turbines to clear the intrusion and restore full pipe flow. If CCTV reveals the pipe is cracked or compromised, we recommend pipe relining to seal the entry points permanently. Without repair, tree root blockages typically recur within 6 to 12 months.
Cause 2 of 8
2
Grease blockages are the leading cause of blocked kitchen sinks in both residential and commercial properties.
What Happens
When cooking grease, fats, and oils are poured down the kitchen drain, they’re liquid from the heat. As they travel through the pipe and cool, they solidify and coat the internal pipe walls. Over time, these sticky deposits trap food particles, soap residue, and other debris, progressively narrowing the pipe diameter until water can no longer pass through.
How We Fix It
Hydro-jetting is the most effective method for grease blockages. The high-pressure water stream — at up to 5,000 PSI — strips solidified grease from the full internal circumference of the pipe, restoring it to original diameter. Electric eels can punch through grease blockages, but only clear a channel through the centre — the grease remains on the pipe walls and the blockage returns faster.
Prevention
Never pour cooking oil, grease, or fat down the drain. Let it cool in a container and dispose of it in the bin. Run hot water through your kitchen drain for 30 seconds after washing up.
Cause 3 of 8
3
Bathroom drains — particularly showers, bathtubs, and basin sinks — are highly susceptible to hair and soap scum accumulation.
What Happens
Hair falls into the drain during showers and washing and binds with soap residue to form dense, matted clumps. These clumps catch on pipe walls, drain fittings, and P-traps, creating a growing mass that restricts water flow. Over weeks and months, the accumulation worsens until the drain blocks completely.
How We Fix It
Minor hair blockages can sometimes be cleared with a plunger or manual extraction — see our DIY drain clearing guide for safe methods you can try at home. For deeper or more compacted hair blockages, our plumbers use electric eels and drain rods to break apart and remove the matted build-up, followed by a hot water flush.
Prevention
Install drain screens in showers and bathtubs to catch hair before it enters the pipe. Clean screens weekly. A monthly flush with bicarbonate of soda and white vinegar helps prevent soap scum accumulation.
Cause 4 of 8
4
Flushing items that don’t break down in water is one of the fastest ways to cause a blocked toilet or a blockage deeper in the sewer line.
What Happens
Wet wipes (even those labelled “flushable”), sanitary products, cotton buds, nappies, dental floss, and children’s toys are all common culprits. These items don’t dissolve in water. They lodge in pipe bends, junctions, and narrower sections of the drainage system, creating an immediate or progressive blockage that traps everything behind it.
How We Fix It
CCTV inspection to locate the foreign object, followed by hydro-jetting or mechanical clearing to dislodge and flush it from the system. For persistent blocked toilet issues, we may need targeted extraction or access pit excavation if the object is too large or firmly lodged to clear by jetting alone.
Prevention
Only flush the three Ps — pee, poo, and (toilet) paper. Keep a bin in the bathroom for everything else.
Cause 5 of 8
5
Pipe failure is a common cause of recurring blockages that keep coming back despite repeated clearing.
What Happens
Ageing pipes deteriorate over time from ground movement, tree root pressure, corrosion, and general wear. Cracked pipes allow soil and debris to enter the drainage system. Collapsed sections create a physical barrier that traps waste and causes backflow. Misaligned joints from ground settlement create lips and steps inside the pipe where debris accumulates.
How We Fix It
CCTV inspection is essential to identify the type, location, and extent of pipe damage. For cracked or root-damaged pipes that are still structurally intact, pipe relining is the preferred solution — a structural epoxy liner is inserted and cured in place, creating a new pipe within the old pipe with a 50-year life expectancy and no need for excavation. For fully collapsed pipes, targeted excavation and pipe replacement of the affected section may be necessary.
Cause 6 of 8
6
Blocked stormwater drains are especially common during Sydney’s heavy rainfall periods and after storms.
What Happens
Leaves, dirt, mulch, sediment, and garden debris wash into stormwater drains and gutter systems during rain. If grates aren’t kept clear, this material accumulates inside the pipe, reduces flow capacity, and eventually causes a complete blockage. Tree roots also commonly invade stormwater pipes through cracks and joints.
How We Fix It
We clear stormwater blockages using hydro-jetting to flush debris from the pipe, followed by CCTV inspection to check for root intrusion or pipe damage that may have contributed to the blockage. For properties with recurring stormwater issues, we recommend a scheduled maintenance plan with regular grate clearing and hydro-jet flushing.
Prevention
Keep stormwater drain grates clear of leaves and debris, particularly before heavy rain. Trim overhanging vegetation near stormwater drains. Schedule a professional stormwater inspection before winter.
Cause 7 of 8
7
Hard water deposits narrow pipes gradually over years.
What Happens
In areas with harder water, mineral deposits — primarily calcium and magnesite — accumulate on the internal walls of pipes, reducing the internal diameter and creating rough surfaces that trap other debris. Scale build-up is most common in older galvanised steel and copper pipes.
How We Fix It
Hydro-jetting at high pressure strips mineral scale from pipe walls and restores flow. For severely scaled pipes that have lost significant internal diameter, pipe relining or replacement may be recommended.
Cause 8 of 8
8
Incorrectly installed pipes are a hidden cause of chronic, recurring blockages.
What Happens
Pipes installed with insufficient fall (gradient), improper joint connections, or undersized diameters create low-flow zones where waste and debris settle and accumulate instead of flowing through to the sewer main. This is a common issue in renovated properties where plumbing has been modified by unlicensed tradespeople.
How We Fix It
CCTV inspection identifies sections with inadequate fall or poor joint connections. Depending on severity, the solution may involve pipe relining to smooth the internal surface, or targeted excavation and reinstallation of the affected section with correct gradient.
If your drain is blocked and the cause isn’t immediately obvious — or if the blockage keeps returning — it’s time to call a licensed plumber. DIY methods are effective for minor, surface-level blockages, but anything deeper requires professional CCTV inspection, hydro-jetting, and specialist clearing equipment to diagnose and resolve properly.
What Happens When You Call
Proximity Plumbing offers a $0 call-out fee across Sydney. We attend your property, inspect the blockage using CCTV, and provide an upfront fixed-price quote before any work begins. If you choose not to proceed, you owe nothing.
30-minute responseEastern Suburbs guarantee.
24/7 availabilitySame flat rate, day or night.
Transparent pricingFixed-price quote before any work.
Whatever the cause, we’ll diagnose it with CCTV, clear it properly, and tell you exactly what it’ll take to stop it coming back — with no call-out fee for our time.
✓ $0 Call-Out Fee
✓ Transparent Flat-Rate Pricing
✓ No Overtime Fees
✓ 30-Min Response
✓ 24/7 Availability
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