A blocked or smelly gully trap is one of those jobs that sounds worse than it is — but only if you go about it the right way. With a bit of preparation and the right tools, you can clean a gully trap without turning your yard into a sewage swamp. Here's how to do it cleanly and safely.
What Is a Gully Trap and Why Does It Block?
A gully trap is a small, ground-level drainage fitting — usually made from PVC or ceramic — that collects wastewater from laundry tubs, kitchen sinks, and sometimes shower or bath overflows before it enters the underground drain. It has a water seal at the bottom that acts as an odour barrier, similar to the trap under your sink.
Gully traps block when grease, soap scum, hair, food scraps, or garden debris build up in the trap bowl or in the pipe leading away from it. In older NZ homes, ceramic gully traps are common and can crack or partially collapse, making blockages worse.
Tools and Supplies You'll Need
Gather everything before you start so you're not running back and forth:
- Rubber gloves (heavy-duty, elbow-length if possible)
- Safety glasses — splashback is a real risk
- Old clothes or a disposable apron
- A bucket and a small hand scoop or old cup
- Garden hose with a good flow
- A stiff-bristled brush (an old toilet brush works well)
- Drain rods or a plumber's hand auger (available from Bunnings or Mitre 10)
- Enzyme-based drain cleaner or baking soda and white vinegar for deodorising
- A tarp or plastic sheeting to protect the surrounding area
Avoid using caustic soda or harsh chemical drain cleaners in a gully trap — they can damage older ceramic traps and are hazardous to handle.
Step-by-Step: Cleaning a Gully Trap Neatly
1. Protect the Area First
Lay a tarp or old plastic sheeting around the gully trap. This is the single biggest step to avoiding a mess. If the trap is badly blocked and water is sitting in it, use your scoop and bucket to remove as much standing water and debris as possible before you start disturbing anything.
2. Put On Your PPE
Put on your gloves and safety glasses before you touch anything. Wastewater contains bacteria and pathogens — WorkSafe NZ recommends treating all wastewater as a contamination risk. Wash your hands thoroughly when you're done.
3. Remove the Grate and Scoop Out Debris
Lift off the gully trap grate (it usually just lifts free). Use your scoop to remove any accumulated sludge, hair, or food waste from the trap bowl and place it directly into a bucket — not onto the lawn. Tie off the bucket in a rubbish bag for disposal.
4. Rod or Auger the Outlet Pipe
If the blockage is in the pipe leading away from the trap rather than in the bowl itself, you'll need to use drain rods. Feed the rods into the outlet at the bottom of the trap and work them back and forth with a clockwise twisting motion to break up the blockage. Always twist clockwise — anticlockwise can unscrew the rod joints and leave them stuck in the pipe.
5. Flush Thoroughly With the Hose
Once the blockage is cleared, flush the trap and pipe with a strong flow of water from your garden hose. Keep the hose nozzle low and pointed into the trap — not spraying upward — to avoid splashing. Let the water run for a couple of minutes to confirm the drain is flowing freely.
6. Scrub and Deodorise
Scrub the inside of the trap bowl with your stiff brush. Pour a cup of baking soda followed by a cup of white vinegar into the trap, let it fizz for 10 minutes, then flush again with water. This helps neutralise odours without damaging the trap or the environment.
7. Replace the Grate and Clean Up
Refit the grate, roll up your tarp carefully (debris side in), and bag everything for the bin. Hose down the surrounding area and wash your gloves before removing them.
How Often Should You Clean a Gully Trap?
As a general guide, inspect and clean your gully trap every 6–12 months, or sooner if you notice slow drainage, gurgling sounds, or odours. Homes with large households or those that discharge kitchen waste to the gully trap may need more frequent attention.
NZ Building Code Considerations
Gully traps are part of your home's sanitary drainage system, which is covered under the NZ Building Code clauses G13 (Foul Water) and E1 (Surface Water). Cleaning and unblocking your own gully trap is generally considered maintenance and does not require a building consent. However, any work that involves replacing, relocating, or modifying the trap or connected pipework is restricted sanitary plumbing work and must be carried out by a licensed tradesperson registered with the Plumbers, Gasfitters and Drainlayers Board (PGDB). Always check with your local council if you're unsure.
When to Call a Professional
Call a licensed drain cleaner or drainlayer if:
- The blockage won't clear after rodding
- You can see the trap is cracked, broken, or sunken
- Multiple fixtures in the house are draining slowly at the same time (this suggests a main drain blockage)
- There is sewage backing up into the trap from below
- The trap is in an awkward or confined location
A professional will have CCTV drain inspection equipment to identify the exact cause and location of the problem. You can find qualified local drain cleaners on tradedirectory.co.nz.
Master Plumbers
Certifying Plumber
SiteWise
