A blocked drain running beneath a concrete path is frustrating, but in many cases you can clear it yourself without touching the concrete at all. The key is accessing the drain through existing inspection openings (also called rodding eyes or inspection chambers) and using the right tools to break up and flush away the blockage.
Understand What You're Dealing With First
Before you start, figure out what type of drain is blocked. In NZ homes there are typically two systems:
- Stormwater drains – carry rainwater from roofs, paths and paved areas to the street or a soakpit.
- Wastewater (foul) drains – carry sewage from toilets, sinks and showers to the council sewer or a septic tank.
Knowing which system is blocked matters because the two must be kept separate under the NZ Building Code (clauses E1 and G13). If you're unsure, check with your local council or a licensed drainlayer.
Safety First
Wastewater drains contain raw sewage and harmful bacteria. Always wear rubber gloves, safety glasses and old clothing. Wash your hands thoroughly afterwards. If you smell gas near any drain opening, stop work immediately and call your gas supplier. Never enter a confined space such as a deep inspection chamber — this is a WorkSafe NZ requirement and can be fatal.
Tools You'll Need
| Tool | What it does |
|---|---|
| Drain rods (set) | Flexible rods screwed together to push through blockages |
| Plunger (drain type) | Creates suction to dislodge soft blockages |
| Garden hose with jet nozzle | Flushes debris once loosened |
| Wet/dry vacuum | Sucks out standing water or debris |
| Torch and mirror | Helps you see inside inspection chambers |
| Rubber gloves & eye protection | Personal safety |
Drain rod sets are available from Bunnings or Mitre 10 for hire or purchase.
Step-by-Step: Clearing the Blockage
1. Locate the Inspection Chamber or Rodding Eye
Walk the line of the drain and look for a round or square cover set into the ground near the path. These are usually plastic or cast iron. If there's no accessible chamber near the blocked section, you may need a professional with a drain camera.
2. Remove the Cover Carefully
Use a flat-head screwdriver or drain key to lift the cover. Set it aside safely. Check the water level inside — if it's full to the brim, the blockage is downstream (away from the house). If it's empty, the blockage is upstream (between the chamber and the path inlet).
3. Rod Towards the Blockage
Screw two or three drain rods together and feed them into the pipe in the direction of the blockage. Always turn rods clockwise as you push — turning anticlockwise can unscrew them and leave rods stuck in the pipe, which is a costly mistake.
Apply firm, steady pressure and a gentle twisting motion. You'll often feel the blockage give way. Common culprits under paths include:
- Compacted leaf litter and silt
- Tree root intrusion (very common in NZ with large natives nearby)
- Collapsed or cracked pipe sections
4. Flush With Water
Once you feel the blockage clear, run a garden hose at full pressure into the upstream end of the drain to flush debris through. Check the inspection chamber to confirm water is flowing freely.
5. Use a High-Pressure Jet Washer (Optional)
For stubborn silt or grease build-up, a drain jet attachment on a pressure washer works well. Feed the hose into the pipe and let the forward-facing jets pull it through while blasting debris loose. This technique is sometimes called hydro-jetting.
6. Replace the Cover and Clean Up
Replace the inspection chamber cover securely. Rinse all tools with clean water, disinfect if used on a wastewater drain, and dispose of any debris in your rubbish (not the garden).
What If the Drain Is Still Blocked?
If rodding doesn't work, the problem may be:
- Tree root intrusion requiring mechanical cutting or root treatment
- A collapsed or offset pipe under the concrete — this will need excavation
- A blockage beyond your accessible section of pipe
In these situations, a licensed drainlayer with a CCTV drain camera can pinpoint the exact problem without unnecessary digging.
Do You Need a Building Consent?
Simply clearing a blockage does not require a building consent. However, if the drain pipe itself needs to be repaired or replaced, this is restricted building work in most cases and may require a consent depending on the scope. Always check with your local council before doing any drain repairs. The MBIE Building Performance website has useful guidance on Schedule 1 exemptions.
When to Call a Professional
Call a licensed drainlayer (registered with the Plumbers Gasfitters & Drainlayers Board) if:
- Rodding doesn't clear the blockage after a couple of attempts
- You suspect a collapsed, cracked or root-damaged pipe
- There is no accessible inspection chamber near the blockage
- Sewage is backing up into the house
- The drain runs close to your property boundary or connects to the council main
Drainlaying work on wastewater and stormwater connections is restricted work under the Plumbers, Gasfitters, and Drainlayers Act 2006 and must be carried out by a licensed professional. You can find qualified local drain cleaners and drainlayers on tradedirectory.co.nz.
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