Locating a drain blockage doesn't always require expensive camera equipment. With a bit of patience and some simple tools, you can narrow down where the problem is — saving time and money when a professional drainlayer does arrive. Here's how to do it methodically and safely.
Start With the Symptoms: What Is (and Isn't) Draining?
The first step is observation. Walk through your home and test every fixture — sinks, basins, showers, baths, toilets, and laundry tubs. Note which ones are draining slowly or not at all.
- Single fixture blocked (e.g. just the kitchen sink): The blockage is almost certainly in the trap or branch drain directly serving that fixture. This is usually a DIY-accessible problem.
- Multiple fixtures on one side of the house blocked: The blockage is likely in a shared branch line connecting those fixtures.
- All fixtures in the house backing up or gurgling: The blockage is probably in the main drain between your house and the street, or near the inspection chamber (also called a manhole or rodding eye).
This simple process of elimination is your most powerful tool.
Check Your Inspection Chambers and Rodding Eyes
Most NZ homes built after the mid-20th century have at least one inspection chamber (a concrete or plastic access point) somewhere between the house and the boundary. Older villas and bungalows may have cast-iron rodding eyes — screw-cap access points — at changes of direction in the drain.
- Locate your inspection chambers — check your property file at your local council if you're unsure where they are. Some councils provide drainage plans online.
- Carefully lift the lid (use gloves and a flat-bladed tool — lids can be heavy).
- Look inside. If the chamber is full of water or sewage, the blockage is downstream (between that chamber and the next one, or at the street connection). If the chamber is empty or flowing freely, the blockage is upstream, between the house and that chamber.
- Work your way along the drain, checking each chamber in turn, until you find where water is backing up.
This method can pinpoint the blocked section to within a few metres without any specialist equipment.
Use a Drain Rod or Garden Hose to Probe
Drain rods (flexible fibreglass rods that screw together) are available from Bunnings or Mitre 10 for a modest cost and are a worthwhile investment for any homeowner. Feed them into a rodding eye or inspection chamber and push gently in the direction of the suspected blockage. When the rod meets resistance, you've found the approximate location.
Alternatively, run a garden hose into the drain and push it as far as it will go. Where it stops is a rough guide to where the blockage sits. Mark the hose with tape at the point it enters the drain, then measure the length — this gives you a distance to count off along the drain line outside.
Check the Trap First for Single-Fixture Blockages
If only one fixture is affected, always check the trap (the U-shaped pipe beneath the sink or basin) before assuming the blockage is further down the line.
- Place a bucket under the trap.
- Unscrew the trap's slip-joint nuts (or use a wrench if they're tight).
- Remove the trap and clear any debris.
- Refit and test.
This fixes the majority of kitchen and bathroom sink blockages and costs nothing.
Listen and Look for Clues
Drains often give away their problems if you pay attention:
- Gurgling sounds from a floor waste or toilet when you run water elsewhere suggests a partial blockage creating a vacuum in the line.
- Slow drainage in multiple fixtures that gets worse over time points to a gradual build-up (often fat, grease, or tree roots) in a shared line.
- Wet patches or sunken ground in the garden above where a drain runs can indicate a collapsed or blocked pipe — a more serious issue requiring professional assessment.
- Sewage smells outside near the boundary may point to a blocked or overflowing inspection chamber.
Know Your Drain Layout
Understanding roughly where your drains run makes the whole process easier. Your property file (available from your local council) should include a drainage plan. MBIE Building Performance has guidance on accessing building records. For newer homes, the drainage layout may also be in your LIM report.
Safety First
Always wear rubber gloves and wash your hands thoroughly after working near drains. Sewage contains harmful bacteria. Never lean directly over an open inspection chamber — toxic gases including hydrogen sulphide can accumulate in confined spaces. If you smell something unusual or feel unwell, step back immediately and get fresh air. WorkSafe NZ has guidance on confined space hazards.
Do not use chemical drain cleaners repeatedly — they can damage older pipes and are harmful to the environment.
When to Call a Professional
Drainlaying is restricted work under the Plumbers, Gasfitters and Drainlayers Act 2006. While homeowners can clear blockages in their own home's internal drains, any work that involves cutting into, replacing, or relaying drain pipes — especially underground or at the boundary — must be carried out by a licensed drainlayer. Check that your tradesperson is registered with the Plumbers Gasfitters & Drainlayers Board.
Call a professional drainlayer if:
- You cannot locate or clear the blockage yourself.
- Multiple chambers are backing up.
- You suspect a collapsed pipe or tree root intrusion.
- There is sewage surfacing in your yard.
- The blockage is in the public drain at or beyond your boundary (this is your council's responsibility — contact them directly).
A qualified drainlayer will have CCTV equipment, high-pressure water jetting, and the expertise to diagnose and fix the problem correctly. You can find licensed local drainlayers on tradedirectory.co.nz.
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