A slow drain, a sewer smell in the basement, a patch of lawn that stays green in August. Each of those tells you something is wrong with your sewer line. None of them tells you where.
That’s the job of sewer line leak detection: finding the exact spot and depth of the failure before anyone picks up a shovel. It’s the step that decides whether the repair is a single small opening, a liner pulled through the old pipe, or something larger. Get the location wrong and the repair lands in the wrong place, or gets sized for a problem you don’t have.
This guide walks through how we find a sewer line leak or break at Arrow Sewer & Drain: the tools, the order we use them in, and what changes depending on where along your line the failure sits.
If the water you’re worried about is coming from a supply line (a spiking water bill, a hissing wall, a wet spot that isn’t sewage), that’s a different system and a different test. See our leak detection service for pressurized water lines.
Why Location Matters As Much As The Condition
Every sewer failure has two answers: what went wrong, and where. Most of what goes wrong comes down to the age of the pipe and the soil around it, which produce the seven conditions behind nearly every sewer repair we do: roots, cracks, corrosion, material fatigue, offsets, bellies, and collapse.
The where is just as important, because location decides four things before the condition does:
- Access. A break under the lawn and a break under the basement floor can be the same crack. One is reached with a shovel; the other means cutting concrete or working from inside the pipe.
- Method. Some repair methods can reach a section and some can’t. The connection to the town’s main is the one point trenchless methods generally can’t reach.
- Cost. What sits on top of the pipe (grass, a driveway, a finished basement, a county road) often costs more to open and restore than the pipe repair itself.
- Ownership and permits. In most New Jersey towns you own the line from the foundation to the main, but anything under a sidewalk or road brings permits, markouts, and sometimes a police detail.
That’s why sewer line leak detection isn’t finished until the failure has a measured distance and depth. “Somewhere in the yard” isn’t a location you can price or plan around.
How We Find A Sewer Line Leak
There’s no single leak-detection tool. There’s a sequence, and each step narrows the search for the next one. On most residential calls, the first four steps find the failure. The last three come in when the first four leave a question open.
- Get into the line. We start at a cleanout. Our standard is three per home (basement, yard, and curb) because each one gives us a different starting point. Older NJ homes often have one or none, so we may come in through a house trap or a pulled toilet instead. If you’re not sure what you have, our sewer cleanout guide shows what to look for.
- Clear the line if it’s blocked. A camera can’t see through standing water or a clog. When the line is backed up, we clear it first with hydro jetting, which also strips away buildup that can hide a crack or separated joint.
- Run the camera. This finds the failure and identifies it.
- Locate it from the surface. This turns “40 feet in” into a mark on the ground with a depth.
Camera Inspection
For a sewer line, the camera is the foundation of any honest sewer line leak detection. A waterproof camera on a flexible push rod goes in through the cleanout and records continuous video of the pipe’s interior, with a footage counter showing how far in it is.
On screen, a crack reads as a dark line along or around the pipe wall: hairline if it’s early, an open gap with soil or roots showing through if it isn’t. The same pass shows separated joints, root intrusion, corrosion, and bellies holding water. Without the camera, anyone telling you they’ve found a leak is guessing at both its location and its cause. Our guide to what sewer cameras show walks through the footage in more detail, and our sewer camera inspection service page covers the visit itself.
Electronic Line Locating
The camera head carries a small radio transmitter called a sonde. Once the camera stops at a defect, the technician walks the surface with a handheld receiver until it pinpoints the camera’s position, usually within an inch or two horizontally, with a depth reading.
This is the step that turns “there’s a problem somewhere in your line” into “the break is 32 feet from the basement cleanout, 4 feet down, under the edge of the driveway.” That difference often decides whether the repair is a targeted spot fix or a full replacement.
Acoustic Leak Detection With Geophones
A geophone is a sensitive ground microphone. The technician moves it along the surface over the pipe’s path, listening for the sound of liquid escaping. It’s most useful when a leak is suspected but doesn’t show clearly on camera: a hairline crack that only opens under flow, or a defect below the waterline in a partly full pipe. It’s also a fast way to narrow down a location under hardscape before anything gets opened. Telling a leak apart from traffic noise or flow in nearby pipes takes training, which is why the reading matters as much as the tool.
Hydrostatic And Pressure Testing
The section of line is isolated and filled or pressurized, then watched for a drop. A drop confirms a leak exists even when the camera footage is ambiguous. On sewer lines we use it mainly to confirm a suspected hairline leak, and it’s often paired with geophone work to pinpoint where the leak the test confirmed sits.
Smoke Testing
Non-toxic smoke is forced into the line, and we watch where it comes out: at the surface over the pipe, through foundation seams, or around a basement fixture. Smoke testing is especially useful when there’s an on-and-off sewer smell and the camera hasn’t found an obvious source. If that’s your situation, it’s also worth reading whether sewer gas is dangerous and what levels warrant concern.
Dye Testing
Colored dye goes into a fixture or drain, and we watch for it surfacing where it shouldn’t: in the yard, a storm drain, or a sump pit. Dye testing confirms a suspected leak path and answers questions records can’t, like whether a downspout or floor drain is tied into the sewer.
Hydro-Excavation For Verification
We bring in hydro excavation when the marked section sits in a tight utility corridor: a sewer line running alongside gas, water, electric, or fiber lines, often near the street or under a driveway apron. Digging there with a backhoe or shovel risks striking a live utility. Pressurized water and a vacuum loosen and remove the soil without cutting through anything buried, so we can expose the sewer pipe at the exact spot the camera flagged and leave the surrounding lines untouched.
The same approach confirms problems that started outside the pipe: a belly, a settled section, or a separated joint with no clear cause in the pipe itself. Once the pipe and its bedding are visible, we can judge the soil directly before recommending a repair.
Choosing The Right Combination
The right mix depends on the symptoms:
- Recurring backups or a green stripe in the yard: camera plus locating, almost every time.
- An on-and-off sewer smell with no other symptoms: camera, then smoke testing if the camera comes up clean.
- A suspected hairline leak the camera can’t confirm: pressure testing plus geophones.
- A defect that looks soil-driven, or a break in a tight utility corridor: camera plus hydro-excavation before any repair is priced.
A contractor who only owns one of these tools tends to fit every problem to it. We run all seven, so the method follows the symptoms.
Where Sewer Lines Fail: Five Zones From Your Floor To The Street
Your sewer line passes through five zones on its way from the house to the town’s main. The failures in each zone tend to look different, get detected a little differently, and lead to different repairs.
1. Under The Basement Floor Or Slab
What fails here: The building drain runs beneath the concrete before it leaves the house. In older New Jersey homes it’s usually cast iron, which corrodes from the inside until the wall thins, cracks, or scales shut. Settling fill under a slab can also leave a low spot that holds water.
How we find it: Camera from the basement cleanout, then the sonde marks the defect on the floor surface with a depth. A sewer smell near a floor drain with a clean camera run is where smoke testing earns its place.
What it usually leads to: Lining from inside the pipe, coating for corroded but sound cast iron, or one targeted cut at the marked spot instead of trenching the whole floor. Our guide to a broken sewer pipe under the slab covers this zone in depth.
2. At The Foundation Wall
What fails here: Where the pipe passes through the foundation, the house and the surrounding soil settle at different rates. That shear point is a common place for cracks, separated joints, and root entry. Many pre-1972 NJ homes also have a house trap near this point, which can hold debris and slow drainage on its own.
How we find it: The camera shows the transition as the pipe leaves the building, and the footage counter tells us whether the defect sits inside the wall, just outside it, or under the basement floor.
What it usually leads to: Often a small excavation just outside the foundation, or a liner that runs through the wall section without disturbing it.
3. Under The Yard
What fails here: The longest stretch, and where most of the classic failures show up: root intrusion at clay joints, offset sections from freeze-thaw and settling, and bellies where the pipe has lost its slope.
How we find it: Camera plus locating handles most yard failures. A green or soggy stripe on the lawn is a strong surface clue. When the camera suggests the soil moved rather than the pipe failed, hydro-excavation confirms it before a repair is chosen.
What it usually leads to: This is where trenchless sewer repair does most of its work, because the pipe usually has a followable path and room for an access pit at each end.
4. Under The Driveway, Sidewalk, Or Road
What fails here: The same failures as the yard, under a much more expensive surface. Paved sections also see more load and vibration, so settlement and cracking show up here earlier.
How we find it: Precision matters most in this zone, because every extra foot of opening costs more to restore. Geophones help narrow a location quickly under hardscape, and the sonde mark keeps any opening as small as possible.
What it usually leads to: Trenchless methods whenever the pipe allows, since they avoid cutting pavement. Anything under a sidewalk or road brings permits and markouts, which we handle, and sometimes a town-required police detail.
5. At The Tap
What fails here: The tap is where your lateral connects to the town’s main, usually under the street. Root intrusion, a separated connection, or a collapsed saddle at the main are the common failures.
How we find it: The camera shows the transition into the main, and locating gives the depth, which at the street is often the deepest point on the line.
What it usually leads to: The tap is the one point trenchless methods generally can’t reach, so it usually calls for a dedicated sewer lateral connection repair. Where your responsibility ends and the town’s begins varies by municipality, so we confirm that before any work is planned.
When The Camera Can’t Get Through
Sometimes the camera stops before it finds anything clearly. That stop is information in itself, and the first job is figuring out what caused it.
- Debris or a heavy clog. Grease, wipes, scale, or a root mass can block the camera without any structural failure behind them. We clear it and run the camera again. If you’re dealing with repeated stoppages, our guide to a main sewer line clog covers what causes them.
- Broken pieces of pipe. When a section has broken apart, loose fragments can sit in the line and stop the camera short of the real damage. Before any fix, we use a robotic tool to grab and pull those broken pieces out, so the camera can see what’s beyond them and the line can drain in the meantime.
- A true collapse. If the pipe itself has caved in, nothing passes. The locator still marks exactly where the camera stopped, which tells us where the collapse begins.
- Coming in from the other end. When one direction is blocked, we run the camera from a second cleanout toward the stopping point. That shows how long the damaged section is from both sides.
A line the camera can’t pass doesn’t always mean digging. It does mean the repair decision shifts toward methods that don’t depend on the old pipe’s path. Our guide to a collapsed sewer line walks through those options.
What Detection Tells You, And What It Doesn’t
Good sewer line leak detection gives you three things: the failure, its exact location, and its depth. What it doesn’t automatically give you is why the pipe failed there, and that’s the part that decides whether a repair will hold.
A leak through a corroded section of cast iron is a pipe-side failure. The pipe wall gave out, and lining or replacing the pipe solves it.
A leak at a joint that pulled apart because the soil underneath shifted is a soil-side failure. The bedding moved and dragged the pipe with it. Lining or replacing the pipe in the same soil sets up the same failure on roughly the same timeline.
So the honest next question after “where is it?” is “what is the camera telling us about the ground around it?” Sometimes the answer is a clean pipe-side defect with a targeted repair. Sometimes the pipe is fine but the bedding has moved, and the soil needs to be checked before anyone recommends a method. Both answers are legitimate. A contractor who only ever gives the first one isn’t reading the footage all the way through.
Can You Find A Sewer Leak Yourself?
You can tell a sewer line is likely broken. Finding exactly where takes equipment. Here’s what a homeowner can safely notice:
- Surface clues. A green, soggy, or sunken stripe across the lawn, or pavement settling along the path between the house and the street.
- Inside the house. A sewer smell in the basement that doesn’t clear, or a basement floor drain backing up when upstairs fixtures run.
- Plumbing behavior. Several fixtures draining slowly at once, gurgling, or backups that come back after the line is cleared.
- Pests. Rodents or insects near the foundation with no other explanation can point to a break that’s open to the soil.
One pattern helps narrow things down. A problem at a single fixture usually points to that fixture’s branch line. A problem across the whole house usually points to the main line. Our guide to cracked or broken sewer pipe signs goes through each symptom in more detail.
Where DIY stops: digging to “take a look” usually means guessing at a spot and finding intact pipe. Rented cameras don’t come with locators or the training to read footage, and a backed-up line can expose you to sewage. None of these signs is usually an emergency on its own, but a whole-house backup or sewage coming up through a floor drain is a reason to call the same day.
What Happens After The Break Is Found
Once detection has pinned down where the failure is and what kind it is, the repair options sort into a few familiar paths:
- One isolated defect on otherwise sound pipe (a single crack, a separated joint, roots at one spot): often a targeted spot repair, or a small opening at the marked location.
- Wear along a longer run (multiple cracks, roots at several joints, corroded cast iron): lining creates a new pipe inside the old one and seals the joints that were leaking.
- A pipe too far gone to line, but with a followable path: pipe bursting replaces it along the same route.
- No followable path left: a new route has to be bored or dug.
- A soil-side failure: excavation, so the bedding can be rebuilt and the pipe re-laid at the right slope. A trenchless repair alone won’t fix why the pipe moved.
Our guide on which trenchless method fits which condition goes deeper on that choice. Every one of these paths falls under our main sewer line repair service. That matters for one practical reason: when the same company runs the camera and performs every method, the recommendation follows the footage instead of the equipment on the truck.
Cost follows the condition and the location, not the calendar, which is why an estimate comes after the camera, not before. For ranges by condition, our sewer repair cost estimator lets you plug in what the camera found, and financing is available. If you’ve already received a quote that skips past why the pipe failed, a free second opinion costs nothing.
Sewer Line Leak Detection FAQs
Is sewer line leak detection the same as water leak detection?
No. Water supply lines are pressurized, so water leak detection relies mostly on pressure testing and listening equipment. Sewer lines carry waste by gravity, so sewer line leak detection starts with a camera inside the pipe and a locator above it. Some tools overlap, but the starting point and the system are different.
Can you find a sewer leak without digging?
Yes, in nearly every case. The camera finds the failure, and the sonde marks its exact position and depth from the surface. Digging comes later, if at all, and only at the marked spot.
Does a sewer camera inspection show leaks?
It shows what causes them: cracks, separated joints, root entry, corrosion, and missing sections of pipe. A hairline leak below the waterline can be harder to see, which is when pressure testing or geophones are added.
How do I know if my sewer line is broken or just clogged?
A clog that clears and stays clear is usually just a clog. Backups that return soon after cleaning, a smell that won’t go away, or a soggy patch in the yard point to damage. A camera inspection after clearing the line answers the question for certain.
What’s the difference between a smoke test and a dye test?
A smoke test fills the line with harmless smoke to show where gas or air escapes, which is useful for tracking down an odor. A dye test adds color to the water to show where liquid travels, which is useful for confirming a leak path or whether a drain is tied into the sewer.
How long does sewer line leak detection take?
A standard camera inspection with locating is usually done in a single visit. If the line needs clearing first, or the camera result calls for smoke, dye, pressure testing, or hydro-excavation, those can add time or a second visit.
Who is responsible for the sewer line under the sidewalk?
In most New Jersey towns, the homeowner owns the lateral from the house to the connection at the town’s main, including the stretch under the sidewalk. The exact boundary varies by municipality, so we confirm it before any repair is planned.
