A CCTV drain inspection tells you what’s wrong inside a pipe. Sonde locating tells you exactly where that pipe is from above ground, its position and depth, without any guesswork or exploratory digging. For anything that involves excavation, landscaping over a drain line, or precisely planning access points for a reline, sonde locating is the step that connects what the camera found underground to a physical spot in your yard.
What a sonde actually is
A sonde is a small radio-frequency transmitter built into, or attached just behind, the CCTV camera head. As the camera travels through the pipe during a standard inspection, the sonde emits a signal that a handheld receiver can detect from ground level. The operator walks the receiver along the expected pipe route, and the receiver indicates both the sonde’s horizontal position and, with the right equipment, its approximate depth. In practical terms, this means we can mark a defect’s location, or the pipe route itself, directly on the ground while the camera is still inside the pipe, rather than estimating from a written distance measurement alone.
This is different from the distance counter you see in a CCTV report. A distance reading tells you how far the camera has travelled along the pipe from the access point, useful, but it follows the pipe’s actual path, which may bend, angle or run diagonally rather than in a straight line from house to boundary. Sonde locating tells you the pipe’s real-world position on your property, which is what you need if you’re about to dig, plant a tree, lay a new path, or plan exactly where a relining access point should go.
When sonde locating actually matters
Before excavation. If a CCTV inspection has found a collapsed section, an extreme joint offset, or another defect that needs to be dug out and replaced rather than relined, sonde locating marks the exact spot to dig, avoiding unnecessary excavation either side of the actual problem.
Before landscaping or construction. If you’re planning a driveway, retaining wall, deck or garden bed over or near a drain line, sonde locating confirms exactly where the pipe runs and how deep it sits, so you don’t design around guesswork or discover the pipe mid-construction.
Planning relining access points. CIPP relining typically needs access at two points along a pipe run. Sonde locating helps confirm where those access points sit relative to the property, useful when a boundary cleanout’s exact position isn’t obvious, or when a property has had additions or landscaping since the original pipe was laid.
Resolving disputes over responsibility. Where it’s unclear whether a defect sits on your side of a boundary or beyond it, sonde locating gives a precise, on-the-ground answer rather than an estimate based on distance readings alone.
Confirming a pipe’s route where no plans exist. Many older Central Coast properties, particularly those that started as holiday shacks or have been extended multiple times, don’t have accurate drainage plans. Sonde locating maps the actual route as installed, not as originally designed.
How it fits into a normal CCTV inspection
Sonde locating isn’t usually a separate visit. Where the camera head includes a sonde transmitter, locating is carried out as part of the same CCTV inspection: while the camera is travelling through the pipe (or paused at a defect), the operator uses the receiver above ground to mark the corresponding position. For a standard residential inspection this adds a modest amount of time on-site but no separate mobilisation cost. Where a job specifically requires precise depth and position marking, for example ahead of excavation work or construction planning, this is scoped as part of the inspection when booked.
What it costs
Sonde locating is typically included as part of a standard CCTV inspection where the camera equipment has a built-in sonde, so there’s no separate line-item cost for a routine job. Where locating is the primary purpose of the visit, for example, confirming a pipe route on a property with no plans before construction work, this is generally quoted within the same range as a standard residential CCTV inspection, $250-$500, depending on the length and complexity of pipe run to be traced. For excavation-related work following a locate, see the excavation cost drivers in our Drain Relining Cost Guide.
Frequently asked questions
Is sonde locating the same as a “dial before you dig” service? No. Dial Before You Dig identifies registered utility infrastructure (water mains, gas, electricity, telecommunications) in the vicinity of a job. Sonde locating identifies the specific private drain pipe on your property, which isn’t part of the registered utility network. Both are useful, but they answer different questions, and neither replaces the other.
Can sonde locating tell me what’s wrong with the pipe, or just where it is? Just where it is, and roughly how deep. Diagnosing what’s wrong, root intrusion, cracking, joint displacement, comes from the CCTV footage and written defect log, not from the sonde signal itself. For how to read that part of the report, see our CCTV Drain Inspection Report Explained guide.
Do I need sonde locating if I just have one blocked drain and no plans to dig? Not necessarily. If the plan is to clear the blockage and, if needed, reline through existing access points, sonde locating isn’t essential. It becomes relevant once excavation, construction or precise access planning is on the table. Our blocked drain vs broken pipe guide covers how we work out which category your situation falls into in the first place.
How accurate is the depth reading? Modern sonde and receiver combinations are generally accurate to within a small margin under normal soil conditions, though accuracy can vary with soil type, pipe depth and nearby interference from other buried services. For any excavation planning, the reading is treated as a strong guide, with exact depth confirmed carefully as digging approaches the marked point.