A drain cleaning crew learns where a blockage is by feel: the cable or the jetter hose stops advancing. Without a camera they cannot see it and without a locate they cannot say where under the lawn it sits. A sonde fitted behind the nozzle solves the second problem while the cleaning is happening: when the nozzle stops, a second operator walks the receiver to the sonde and marks the spot, and the crew knows whether the obstruction is under the lawn, the driveway or the street before deciding how hard to push. This guide covers how the sonde is fitted, how it is found with the water running and what it does and does not tell the crew.
Quick answer: a sonde for a jetter or drain cable is a rugged 512 Hz transmitter in a stainless or hardened housing, battery-powered, threaded or clamped into the hose or cable a short distance behind the nozzle or cutter, where the jet does not strike it. It is switched on before the hose goes in, located with a standard 512 Hz receiver whenever the nozzle stops, and the position and depth are marked. It tells the crew where the stop is; it does not show what the stop is, which still needs the camera. Sondes for this duty are built to take water pressure and impact and cost more than camera sondes, and they are a consumable on a hard-working truck.
What the sonde is
A battery sonde in a housing designed for the hose or cable: a threaded inline unit that sits between the hose and the nozzle, a clamp-on sleeve that fits over the hose behind the nozzle, or a capsule that rides in a cage. Housings are stainless steel or hardened plastic, sealed to the water pressure the jetter develops and rated for impact against pipe walls. Battery life is a working day or more. Frequency is 512 Hz so that the receiver already on the truck finds it. Sonde transmitters and what a 512 Hz sonde is cover the general case.
Where it mounts
Behind the nozzle, far enough back that the rear-facing jets do not hit it and close enough that its position is the nozzle’s position for practical purposes, usually within a foot. On a cable machine it mounts behind the cutter head on a short section of cable. The sonde adds length and stiffness to the end of the hose, which changes how it takes bends; a crew learns the new behaviour before relying on it.
Surviving the jet
Jetter nozzles run at thousands of psi and the hose drags the sonde over scale, roots and rubble at speed. A camera sonde would not last an hour. Jetter sondes are built for it, and even so they are inspected after each job for cracks, loose end caps and water inside, and replaced when they fail. The receiver check before each job catches a dead one before the hose is in the pipe. Testing a sonde above ground is the check.
Locating with the water running
When the nozzle stops advancing, the jetter operator holds it and the second person locates the sonde from the surface with the receiver in sonde mode, approaching from several directions and marking the peak and depth. The running water does not affect the signal; the pipe’s material and the soil do, as always. Where the nozzle is advancing slowly, the receiver can follow it and mark the route as it goes, which traces the line while cleaning it. Marking a dig covers the locate and the two-person workflow the crew arrangement.
What it tells the crew
Where the stop is, and how deep. Whether the obstruction is under something that makes excavation expensive. Whether the hose has turned up a branch or stayed in the main line, from the route the receiver followed. Whether the stop is at the distance the hose markings suggest, which checks for hose coiled in a fitting. Whether successive stops are at the same place, which suggests a hard obstruction, or progressively further, which suggests a soft one being cut.
What it does not
What the obstruction is. Roots, a collapse, an offset and a belly all stop a nozzle and all feel much the same on the hose. A sonde locate puts a mark on the lawn; only the camera says what is under it. Crews that jet first and camera afterwards use the sonde to decide where to look and the camera to decide what to do. Inspecting before and after jetting covers the sequence, and video jetting nozzles cover the combined tools that do both.
Sonde and camera together
Some crews run the camera behind the jetter on a second reel, watching the cleaning as it happens, with the camera’s own sonde providing the locate; others clean with a sonde on the nozzle and camera afterwards. The combined approach costs a second operator and a camera that gets dirty; the sequential approach costs a second pass. Camera-assisted cleaning and cameras for drain cleaning contractors cover the options.
Interference from the hose and machine
A jetter hose has no metal to speak of and does not affect the locate. A steel drain cable does: it is a long conductor that can carry and re-radiate the sonde’s field, so a locate on a cable-mounted sonde should be approached from several directions and checked against the cable’s markings. A jetter truck parked over the route is a large metal mass; locate away from it. Metal interference covers the symptoms.
Weak signals
A sonde behind a nozzle at the far end of a long run in wet ground may be faint. Raise the receiver gain, pull the hose back to a shallower point, locate there and extrapolate, and replace a sonde whose battery is low. Why a locator cannot find the sonde and weak sonde signals cover the troubleshooting.
Cost and consumables
A jetter sonde costs several times a camera sonde and lasts a season on a busy truck. Batteries are replaced on a schedule, not when they fail. The receiver is the one already used for the camera. For a crew that cleans daily and locates often, the sonde pays for itself in the first dig it moves off a driveway.
Common questions
Can you put a sonde on a jetter?
Yes. Jetter sondes are built to take the pressure and impact and mount behind the nozzle, and they are located with a standard 512 Hz receiver.
Does the water from the jetter affect the sonde locate?
No. Soil, pipe material and nearby metal affect it as they would any sonde; the water does not.
Does a sonde on the nozzle replace the camera?
No. It tells the crew where the stop is; the camera tells them what it is.
Related guides
See a 165 ft self-leveling camera reviewed here, a 100 ft self-leveling camera reviewed here, and flushable sondes.