Wastewater Drainage Problems in Christchurch: Odours and Overflows

Smelly gully traps

The gully trap is the grated dish set into the ground outside your house, usually near the kitchen or bathroom wall, where wastewater from the house joins the drain to the street. It holds a water seal that stops sewer gas coming back up.

If that trap dries out, gets a cracked seal, or the grate is damaged, sewer gas escapes and you get a persistent bad smell near the house, often worse on a hot day or after a dry spell.

Gurgling drains

A gurgling sound from a sink, toilet or shower when another fixture is used is usually a venting problem, a partial blockage, or a drain running below its intended capacity. Air is being pulled back through the water seal in the trap instead of escaping through the vent stack, which is a sign the system isn't breathing properly.

Wastewater overflows

• Water rising out of the gully trap during or after using the toilet or shower
• Toilet water rising close to the rim, or draining away slowly
• Waste backing up into the lowest fixture in the house, often a shower or laundry tub
• A wet patch or smell developing over an underground pipe run

What usually causes it

• Tree root intrusion at an earthenware joint, still the most common cause across older Christchurch suburbs
• A collapsed or bellied section of pipe from ground settlement
• Fat, wipes and food waste building up in the line
• A blocked or damaged vent stack on the roof
• Ground movement affecting the fall of pipe between the house and the street connection

How we diagnose it properly

Rather than guessing from the symptom, we run a CCTV camera down the affected line to see exactly where the problem sits and what's causing it. That's especially important with overflows, since the fix for root intrusion, a collapsed pipe and a simple blockage are all quite different.

Getting it fixed

Depending on what the camera shows, the fix might be a root cut and pipe relining, a spot excavation and repair, a full pipe replacement, or simply clearing and resetting the gully trap seal.

For properties on a septic tank rather than the council network, common in parts of rural Selwyn and Banks Peninsula, an overflow can also mean the tank needs pumping out or is failing, which is worth checking alongside the drain itself.

Frequently asked questions