How do i find where my drains run? (2026)

Overview

Finding where your drains run is partly detective work and partly confirmation. Most homes have separate routes for foul water from toilets, sinks, showers and appliances, and in some places a separate system for stormwater from roofs and surface drains. The aim is to work out which indoor fixtures feed which external pipes, where those pipes join, and where they leave the property. Start with what you can see: toilets, waste pipes under sinks, external downpipes, gully traps, inspection points and manhole covers. Then compare that with the layout of the house and the fall of the land, because drains usually take the shortest practical route downhill to a sewer connection, boundary trap, inspection chamber, treatment system or soakage area. Simple tracing methods such as running water one fixture at a time, listening at inspection points and using safe coloured tracing dye can help identify connections. Avoid guessing and avoid opening sealed systems unnecessarily. If the route disappears under concrete, landscaping or extensions, or if you suspect a blockage, cross-connection or broken pipe, specialist help is usually faster and safer than digging blind. CCTV drain cameras and pipe locators can map buried lines with much more confidence than visual inspection alone.

Who this is for

Homeowners and tenants who want to understand the likely route of household wastewater or stormwater drains before maintenance, renovation, landscaping or discussing a drainage issue with a professional.

What you’ll need

• notebook or phone for a simple sketch
• torch
• gloves
• someone to help run taps or flush fixtures
• safe drain tracing dye or food colouring if suitable
• property plans or building documents if you have them

Before you start

Work out whether you are tracing foul drainage, stormwater, or both, because they may run separately. Check whether any covers or inspection points on your property are safe and accessible, and do not enter confined spaces or remove heavy covers you cannot handle safely. If you rent, ask the landlord or property manager first before opening access points or arranging specialist tracing.

Step-by-step

1. 1

   List every fixture and outside drain point

   Walk through the property and note all toilets, basins, showers, baths, kitchen sinks, laundry tubs, washing machine outlets, dishwashers, floor wastes and any external gullies, downpipes, channel drains, inspection openings or manholes. Mark them roughly on a sketch of the house and section.

   Why: You need a complete starting map before you can work out which connections are likely shared and which are separate.

2. 2

   Find the visible pipe exits from the building

   Look under sinks, behind removable panels and around the outside walls for waste pipes leaving the house. Toilets usually connect to larger discharge pipes; basins, showers and sinks often combine into smaller waste lines before joining the main drain. Outside, look for gully traps where wastewater from sinks or showers may discharge before entering the underground drain.

   Why: Visible exits show the first part of the route and often indicate the direction the buried drain takes once it leaves the wall or floor.

3. 3

   Trace likely routes across the property

   Stand back and look at the layout. Drains commonly run in the most direct practical line toward an inspection chamber, boundary connection, septic tank or treatment unit, while also following the natural fall of the land. Note any clues such as lines of inspection caps, repaired paving, slight settlement, or a grouping of outside waste points that would logically join underground.

   Why: Buried drains are usually installed to keep runs efficient and maintain gravity flow, so likely routing often becomes clearer when you view the whole site.

4. 4

   Test one fixture at a time

   Have one person run water or flush a single fixture while another listens and watches at external gullies, inspection openings or accessible chambers. If appropriate, add a small amount of safe tracing dye to one fixture only and check where the coloured water appears. Repeat methodically, one fixture at a time, and record what connects where.

   Why: Testing fixtures separately helps you distinguish shared pipework from separate branches and reduces confusion.

5. 5

   Check plans and records

   Review any building plans, drainage drawings, renovation documents, pre-purchase reports or septic system paperwork you have. If nothing is available, ask your local council or relevant water authority what property drainage information, as-built records or connection details they hold and how accurate those records are.

   Why: Records can confirm the intended route, the connection point and whether stormwater and wastewater were designed as separate systems.

6. 6

   Use specialist tracing if the route is hidden

   If the line runs under slabs, driveways, mature landscaping or later additions, arrange a qualified professional to use a CCTV drain camera and a locator. They can often follow the pipe, identify junctions, locate blockages or breaks, and mark the route above ground.

   Why: Specialist equipment is the most reliable way to map buried drains without unnecessary excavation.

Why this works

Household drains generally rely on gravity, so they tend to run from each fixture to a branch drain, then to a main drain, then to a sewer connection or on-site treatment system. Visible fittings, fixture testing and official records each reveal part of that path, and CCTV tracing confirms what is hidden underground.

Common mistakes to avoid

• Assuming all water on the property goes into the same drain system
• Running several taps or fixtures at once and then not knowing which route belongs to which fixture
• Confusing stormwater downpipes with foul drainage pipework
• Digging before checking plans, access points and likely routes
• Lifting heavy manhole covers or opening unsafe chambers without proper tools or help
• Using harsh chemicals to try to prove flow direction

Troubleshooting

Compare your options

Alternatives

• Ask a previous owner, builder or neighbour if they know where drains were laid during construction or renovation
• Review pre-purchase inspection reports or septic servicing records if relevant

Pro tips

• Sketch as you go rather than trying to remember routes later
• Label each test clearly, such as kitchen sink, shower or laundry, to avoid mixing results
• Take photos of access points and visible pipes for future maintenance or renovation planning
• If you find a likely route, mark it temporarily above ground before it is forgotten

Safety notes

• Wear gloves and wash up after handling drain covers, traps or wastewater areas
• Do not enter any chamber, tank or pit; confined spaces can contain dangerous gases and low oxygen
• Take care with heavy covers and unstable ground around old chambers
• Stop testing if wastewater backs up inside the home

Legal & regulatory notes

Drainage work, new connections and alterations are commonly regulated and may require qualified tradespeople and consent or approval, depending on your location and the type of system. Property records may be held by your local council or water authority, but they are not always complete. Check local requirements before excavating or altering any drain.

Cost considerations

Basic tracing by observation and record-checking is usually inexpensive. Costs rise if covers need exposing, areas need reinstating, or specialist CCTV and locating services are required. Digging without confirming the route can cost more overall if the wrong area is opened up.

Frequently asked questions

Sources & references

Guidance on this page is traced to documented sources. Last checked 25 September 2026.

• New Zealand Building Code clause G13 Foul Water · government

  Supports the distinction between foul water systems and regulated sanitary drainage requirements in New Zealand.

• New Zealand Building Code clause E1 Surface Water · government

  Supports the distinction between surface water or stormwater drainage and foul drainage.

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