If you can smell sewage in your garden, driveway, or near your home’s exterior, something is wrong with your drainage system. Unlike indoor drain smells that can sometimes be a dry P-trap, outdoor sewer odours almost always need professional attention.

Common Causes of Outdoor Sewer Smell

1. Cracked or Broken Sewer Pipe

Underground sewer pipes can crack from age, ground movement, or tree root pressure. When they break, sewage leaks into the surrounding soil and releases gas.

Signs:

• Persistent sewer smell in one area of the yard
• Patches of unusually lush or green grass
• Soft or soggy ground in dry weather
• Sinkholes or depressions in the lawn

2. Blocked Sewer Line

When the main sewer line is partially or fully blocked, sewage can’t flow to the street. Pressure builds up and forces gas through any weak point — inspection openings, cracked joints, or vent pipes.

Signs:

• Multiple drains inside the house are slow
• Gurgling from toilets or drains
• Smell gets worse after heavy water use (showers, laundry)

3. Damaged Inspection Opening (IO)

Every property has inspection openings (also called overflow relief gullies or ORGs) — round caps at ground level that provide access to the sewer line. If the cap is cracked, missing, or not seated properly, sewer gas escapes.

Check: Walk around your property and look for round plastic or metal caps at ground level. Make sure they’re all in place and sealed.

4. Tree Root Intrusion

Tree roots are attracted to the moisture and nutrients in sewer pipes. They enter through small cracks or joints and can eventually break the pipe apart. Root intrusion creates both blockages and gas leaks.

Signs:

• Recurring drain blockages
• Sewer smell near large trees
• Slow drainage throughout the house

5. Damaged or Blocked Vent Pipe

Plumbing vent pipes on your roof release sewer gas safely above the roofline. If a vent is blocked or damaged, gas can be forced down and out at ground level instead.

6. Stormwater Cross-Connection

In some older Melbourne properties, stormwater and sewer lines can become incorrectly connected. This allows sewer gas to travel through stormwater drains and escape through outdoor grates.

What to Do

Immediate Steps

1. Check inspection openings — Walk around and ensure all caps are in place
2. Look for visible damage — Cracked caps, exposed pipes, soggy ground
3. Note when the smell is worst — After rain? After heavy water use? Constant?
4. Don’t try to unblock a sewer line yourself — Main sewer blockages need professional equipment

Call a Plumber If

• The smell persists for more than a day or two
• You can see sewage on the ground
• Multiple indoor drains are slow or backing up
• There’s a sinkhole or depression forming
• You suspect tree root damage

How We Diagnose the Problem

At Hankook Plumbing, we use:

• CCTV drain camera — We send a camera through your sewer line to see exactly what’s happening inside. This identifies cracks, root intrusion, blockages, and collapsed sections
• Drain location equipment — Pinpoints the exact location and depth of the problem, so we know where to dig (if needed)
• Smoke testing — In complex cases, we can use smoke to trace where gas is escaping

Professional Solutions

Depending on the cause:

• High-pressure water jetting — Clears blockages and root intrusion
• Pipe relining — Repairs cracked pipes from the inside without excavation
• Pipe replacement — For severely damaged or collapsed sections
• IO cap replacement — Quick fix for damaged inspection openings
• Root cutting and prevention — Removes roots and applies treatments to slow regrowth

Don’t Ignore a Sewer Smell

Sewer gas isn’t just unpleasant — it contains methane and hydrogen sulphide, which can be harmful with prolonged exposure. It also means your sewer system isn’t working correctly, and the problem will only get worse.

Call Hankook Plumbing on 0407 756 172 for a professional sewer inspection across Melbourne’s eastern suburbs.