Inside the pipes that keep everything flowing

Aaron Squires stands at the edge of a maintenance hole in Redmond, pulling on a pair of waders. A King County truck sits nearby, with cones marking the work zone and cables running down into the opening below. Squires is part of the King County Wastewater Treatment Division’s 15-member conveyance inspection team, responsible for maintaining and surveying the pipes that spans across our service area.

Below the surface, more than 380 miles of County-owned pipe carry wastewater from homes and businesses to treatment plants. Known as the conveyance system, this network stretches far beyond what most people ever see. If laid end to end, it would run from Seattle to just shy of the California border.

Much of our regional sewer system dates back to the 1960s, with some structures more than a century old. Keeping it reliable takes routine inspection and maintenance. Crews follow a 10-year cycle to inspect every inch of pipe, building a record of how conditions change over time. Some sections are checked more often, about every three years, depending on age, material, or location.

Crew lowers inspection equipment into an open maintenance hole beside a work truck, with safety cones and cables set up on the street.

Lowering equipment into an open maintenance hole to begin a pipe inspection in Redmond.

Today, a three-person crew is inspecting a section of pipe installed 54 years ago. Parked above is a specialized truck equipped with 2,500 feet of cable, connected to a remote-controlled crawler known as the Mudmaster. At about 3 feet long, with inflatable tires and a camera mounted on an articulating arm, it handles most inspections. It is too large to fit through the maintenance hole fully assembled, so the wheels are removed and reattached inside, which requires someone to enter the pipe.

Work begins with a safety check. Crews test the air before entering, using a monitor that measures oxygen levels and detects dangerous gases. Conditions inside confined spaces can change quickly, so the person entering keeps the monitor with them at all times, watching for drops in oxygen or the presence of gases like hydrogen sulfide or methane. Crews are trained for confined space work and treat it with care.

“It’s not something you draw straws for. Everyone takes a turn putting the waders on,” Squires says. “I don’t mind going in as much as I thought I would. It is always a constant temperature, so it feels warm in the winter and cool in the summer.”

Two remote-controlled pipe inspection crawlers sit on the pavement near an open maintenance hole and cable line.

A camera and lights are mounted to the front of the pipe inspection crawler.

Inspection truck parked along a quiet street with cones and equipment laid out near an open maintenance hole.

Inspection crew set up along a neighborhood street, with equipment and traffic control in place.

Close-up of a monitor displaying live video from inside a sewer pipe, showing distance markers and inspection data.

Live video feed shows the inside of a pipe during a remote inspection.

Close-up of hands using a joystick controller to guide a remote inspection crawler through a pipe.

Using a handheld controller to guide the crawler through the system below.

Once assembled, Squires’ crewmate remotely drives the Mudmaster from the truck as the crawler moves through the pipe, sending back live video and data. Crews scan for corrosion, root intrusion, grease buildup, infiltration, and other issues that could affect flow. On a typical day, they inspect around 1000 feet of pipe.

One of the biggest long-term challenges is hydrogen sulfide gas, which forms naturally in wastewater. Over time, the gas can eat away at concrete pipes, creating pits in the surface and exposing reinforcing steel inside. Left unchecked, the pipe structure can weaken. Some crew members focus specifically on managing this program.

The team also inspects maintenance holes, the vertical access points that connect the surface to the pipes below. There are more than 4,000 across King County, ranging from a few feet to more than 100 feet deep.

Using a scanner suspended below a tripod, crews capture detailed 360-degree images, creating a digital record that can be reviewed later without sending someone back down. One recently inspected maintenance hole, built in 1913, is made entirely of brick and remains in good working condition. Others are reinforced concrete, all exposed to shifting soil, moisture, and time. So far, about 700 have been scanned using this newer technology.

Inside a large pipe, a worker stands in shallow water guiding a camera crawler suspended by cables.

The crawler’s wheels are attached after being lowered into the pipe, where shallow flows of wastewater continue moving through the system.

Together, these inspections give crews a clearer picture of the system’s overall health. Cameras document pipe conditions, and when pipes are full, sonar maps what the camera can’t see, measuring buildup and wear below the waterline. What turns up is familiar: corrosion, roots, worn liners, and buildup from fats, oils, grease, and debris. Spotting these issues early helps us stay ahead of larger repairs.

In 2025 alone, the team completed nearly 25 miles of pipe inspection and cleaned more than 40,000 feet of sewer lines.

Mike Sands, supervisor of the conveyance inspection team, said the work is about more than finding problems.

“We’re tracking how the system changes over time so we can be proactive,” he says. “It’s about taking care of the system now, so we can continue serving our communities safely and efficiently for decades.”