A blockage deep underground is one of the trickier drain problems a homeowner can face — a plunger or a bottle of drain cleaner simply won't reach it. The good news is there are several approaches you can try yourself before calling in a professional, and knowing the difference between DIY-friendly tasks and legally restricted drainlaying work will save you time, money, and potential headaches.
Understanding What Causes Deep Drain Blockages
Deep blockages in underground drains are most commonly caused by:
- Tree root intrusion — roots seek out moisture and can crack or infiltrate pipe joints over time
- Grease and fat build-up — accumulates over years and eventually hardens into a solid plug
- Collapsed or misaligned pipes — especially in older homes with clay or concrete pipes
- Foreign objects — items flushed or washed down that travel deep before lodging
- Sediment and debris — particularly after heavy rainfall events common in many NZ regions
Identifying the likely cause helps you choose the right method.
Step 1 — Locate Your Inspection Opening (IO)
Before doing anything else, find your inspection opening (sometimes called a cleanout). This is a capped access point built into your underground drain system, usually at ground level near the house or along the drain run. Removing the cap gives you direct access to the pipe without digging.
If you can't find one, check your property's drainage plan (often held by your local council) or look for a small round or square cap in the ground near downpipes, the kitchen, or bathroom exterior walls.
Step 2 — Try a Drain Rod or Flexible Auger
For many deep blockages, a drain rod set (also called drain rods or drain snakes) is your first practical DIY tool. These are interlocking fibreglass or polypropylene rods you feed down through the inspection opening, adding sections as you go deeper.
How to use drain rods:
- Remove the inspection opening cap carefully — have a bucket ready in case water surges out.
- Attach the plunger head or corkscrew head to the first rod.
- Feed the rod into the pipe, turning it clockwise only as you push forward. Turning anti-clockwise can unscrew the rods and leave them stuck in the pipe.
- Keep adding rod sections until you feel resistance — that's your blockage.
- Work the rod back and forth with a rotating motion to break up or dislodge the obstruction.
- Flush with water from a garden hose to clear debris.
Drain rod sets are available from Bunnings and Mitre 10 as a guide, typically for hire or purchase.
Step 3 — High-Pressure Water Jetting
If rods don't clear the blockage, high-pressure water jetting (hydro-jetting) is the next step up. A jetter uses a powerful stream of water fed through a flexible hose to blast away grease, roots, and debris.
- Compact electric jetters suitable for homeowner use are available for hire from most tool hire shops.
- Larger, trailer-mounted jetters used by professionals can reach much further and generate significantly higher pressure.
- Always wear eye protection and waterproof gloves — the backspray can be forceful.
For tree root intrusion or collapsed pipes, jetting alone may not be enough.
Step 4 — CCTV Drain Camera Inspection
If you've tried rods and jetting without success, or if blockages keep recurring, a CCTV drain camera inspection is the smartest next move. A flexible camera is fed through the pipe to show exactly what's happening underground — root intrusion, pipe collapse, offset joints, or a foreign object.
This is usually a job for a professional drain cleaner, but knowing what you're dealing with means you can make an informed decision about repairs. Some drain cleaning companies offer camera inspections as a standalone service.
What You Can and Cannot Do Legally in NZ
This is important. Under the Plumbers, Gasfitters and Drainlayers Act 2006, drainlaying work — which includes cutting into, joining, replacing, or relocating underground drain pipes — is restricted work that must be carried out by a licensed drainlayer.
As a homeowner, you are generally permitted to:
- Clear blockages using rods, augers, or jetters through existing access points
- Remove and replace an inspection opening cap
You are not permitted to:
- Cut into or repair underground drain pipes
- Install new inspection openings or alter the drain layout
- Connect to the public sewer
Always confirm the scope of permitted work with the PGDB or your local council if you're unsure. Some repair work may also require a building consent — check with your council, as Schedule 1 of the Building Act lists exemptions but these have conditions.
For guidance on what the NZ Building Code requires for sanitary drainage (Clause G13), visit MBIE Building Performance.
When to Call a Professional
Call a licensed drain cleaner or drainlayer if:
- Rods and jetting haven't cleared the blockage after a reasonable attempt
- Multiple fixtures (toilets, sinks, showers) are backing up simultaneously — this suggests a main drain issue
- You suspect tree root intrusion or a collapsed pipe
- There is sewage surfacing in your yard
- The blockage keeps returning within weeks
- You need any pipe repair, replacement, or new access point installed
A qualified drain cleaner will have professional-grade jetting equipment, CCTV cameras, and the expertise to diagnose and fix the problem correctly. You can find licensed drain cleaners and drainlayers in your area on tradedirectory.co.nz.
A Note on Health and Safety
Sewage contains harmful bacteria and pathogens. Always wear waterproof gloves, eye protection, and wash hands thoroughly after any drain work. If sewage has surfaced above ground, treat the area as a biohazard and consider professional clean-up. Refer to WorkSafe NZ for guidance on working safely around wastewater.
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