"So, do you prefer full-immersion or ankle-deep?" Not quite the reply I'd expected from Kent Carlson, the sewer and stormwater field operations manager for the city of Los Angeles, when I requested a tour of the city's new sewer technology.

I'd reached out to Carlson after catching some intriguing photos on his Twitter feed, which showed tiny machines emerging from manholes, their metal teeth seemingly gnawing through wild tangles of roots and branches. It was some serious Teenage Mutant Ninja Turtles shit. Well, I mean stuff. But also, yes, there was shit.

Carlson, of course, was kidding—they don't let journalists strap on hazmat suits and go poop-diving (much to my dismay). But his joke was grounded in fact. As I'd come to learn, Carlson's team uses everything from cute, camera-equipped robots to scary-looking hydro-powered circular saws so that they, too, rarely have to take the full-immersion tour of the sewers.


Attack of the drain bots

When you think of a city's sewer operations, you probably think of one of these trucks pulling up outside your house. Some issues certainly require large-scale interventions, like the giant balloon that LADWP used to choke the massive water main break at UCLA. But in many cases, as Carlson and his team were happy to show me at their headquarters in the San Fernando Valley, what's blocking a sewer drain is something relatively tiny—a crooked PVC pipe, a tree root, a pair of dentures.

"This is how we used to clean sewers," says Carlson, holding up a tool that looks like a rusted bayonet. "We'd take these and hook them together, and the guys would climb down there and cut the roots out." In the past few decades, they graduated to the truck-sized hydrocleaners, which use powerful nozzles to spray jets of water into the drains. Now, the process is both high-tech and precise: Once they've used a tiny camera to view the blockage, they can use a customized hydropowered tool to clear it away.


Carlson's weapons of mass-de-obstruction.

One-by-one, Carlson laid out his secret weapons for me to see, an arsenal of claws, saws, and egg beater-like machines which can be affixed to the trucks' hydropowered nozzles. These are all devices that Carlson and his team have invented to solve very specific problems in the LA. sewer system, each engineered to fit the diameters of LA's standard drains (the average sewer drain is eight inches wide).

Carlson is clearly a professional—he's been with the city for 26 years and before that was a machinist in the Navy. But at this moment it felt as if I was peeking inside a macabre torture chamber.

The crew set up a demonstration to show me a scenario that happens often in the underground world: a PVC pipe feeding sewage from a home slips too far into the larger ceramic drain under the street, causing a backup. This is called a "protruding lateral." Usually, this would require crews to dig up the connection, clear the blockage, and replace the pipe—a costly and messy undertaking. But not anymore.

Cleaning sewers is all about designing the right tool for the right job.

Carlson's team started with one demonstration in a clear plastic pipe: a torpedo-like drill which easily bored into a 2x4. No problems there. Then it was time to fix the protruding lateral. The guys flipped on the high-powered hoses that propelled a spinning diamond-tipped saw down the clay drain. It chewed right through the PVC in minutes.

That was impressive enough, but the big sewer star—and my favorite among them—was an adorable (yes, I can call it adorable) drain bot that reminded me of a squat, Tonka-wheeled Johnny 5. These remote-controlled cameras by Aries have become the saving grace for Carlson and his crew, as they can now get a clear picture of obstructions before they determine how best to clear them using their array of tools. And now these methods have become standard at sewer yards across the county, which has led to a reduction in spills overall.

The all-seeing eye of the sewer is as useful as he is adorable.

"Back in the day, we used to take a lamp, put it down a manhole and crawl down the other side and look up there to see if we could see the lamp to figure out what was in there," says Carlson, shaking his head. Now, with the rotating, articulating lens of this camera, they can zoom and focus anywhere in the pipe, picking up details as tiny as flies. Or, as is more often the case, someone's abandoned dentures.

Carlson has lots of nicknames for his gadgets—many are TMNT-inspired—but he calls this one Ed Norton. Not the Fight Club actor; the character Art Carney played on The Honeymooners who was a New York City sewer worker.

The robots' cameras can tell if something innocent or nefarious is below. Can you tell what's clogging these drains?

This GoPro-like rig for pipes and drains provides astonishingly good image quality to help with repair work, but it also allows the department to document and keep records of what they find and fix. Soon there won't be a single section of LA's sewer system that hasn't been crawled by Carlson's fleet of all-seeing robots. The full magnitude of what the crew is doing here didn't occur to me until much later: They're essentially designing and building their own army of underground drones.

A city mapped by manholes

As in most cities, LA's sewers were built segment by segment over many decades by hundreds of different contractors. The city alone maintains 6,700 miles of these underground mazes. "The conveyance system is such an arena," says Carlson. "Once you flush the toilet, you have to think about how far it travels, then it's treated to the point that it's almost drinkable, and then it exits into the Santa Monica or San Pedro Bay." (That doesn't even include the storm drains, which are a completely different system than the sewage system in LA. Many other cities combine them.)

So perhaps it's not very surprising to hear that the city is still piecing together its sewer maintenance map. Archival data is being gradually imported into a publicly accessible online directory called Navigate LA, which is managed by the Bureau of Engineering, but there are still plenty of gaps. One major part of the sewer system that has not been accurately mapped is the only way to access them: manholes (or the more proper term, maintenance holes).

Spotty data collected from paper archives gives an incomplete picture of what's underground. The street and sidewalk markings used to show the location of utility lines are also a secret language; you can see the code here.

Manholes are often covered by asphalt or dirt, and are sometimes buried completely. Months or years might go by between the times that workers need to locate them, at which point it takes a magic wand-like tool you wave over an area like a metal detector to try to find them. But sometimes when workers get get a call, they'll end up digging up a backyard just to get into the sewer itself.

Carlson has been working to digitize this critical information. He equipped his workers with a GPS app for their phones that allows them to geotag manholes when they're out in the field. So if they locate and tag one once, from then on it will always be in the system.

Carlson pulls open a manhole. It actually doesn't smell at all inside.

The entire system is now centered around these geocoded manholes, with each manhole assigned a particular number based on its location. So Carlson can deploy trucks and other workers based not on a street or an address, but on the manhole that needs to be accessed. "I can see where our vehicles are at all times," he says. "Say, for instance, we got a sewer call in front of your house, I could find the closest truck to get to your house so we don't have any downtime."

The oldest continuously-operating sewer in LA, built beneath Main Street in 1885. Yes, those are cockroaches.

Using Carlson's system, we hop in the truck and navigate to a street in Chinatown, where he wants to show me something special. Thanks to the way they've been digitizing and documenting information, he's been able to do some research, and he's deduced that this is the oldest active sewer in LA. It was built in 1885, back when the latest in sewer innovation was a thick brick lining. It looks positively antique, the equivalent of cobblestones on a street. Carlson says much of the city is still operating with infrastructure that's nearly this old.

Replacing aging sewer lines

The Chinatown brick tunnel might be the oldest operating sewer, but it's not the oldest sewer Carlson's discovered. On the other side of the river, in a Cypress Park yard, are huge cement arches wrapped in rebar. These are cross-sections of a sewer recently removed from a South LA line, which likely date to the 1850s. As you can see, they're still pretty much functional. Even when these were taken out to be replaced with plastic versions, the ceramic-lined tunnels were still in pretty good shape compared to some newer ones, says Carlson.

Carlson points out the ceramic tiles that used to line sewers. They even glazed them.

Repairing or replacing a sewer line is already an arduous task. But then add to that the unique challenge confronting LA: There are 88 separate cities here, all with varying approaches to wastewater. Some have their own sewer districts, some contract with the county. Carlson's team has to work as the unifying force between them all. "Sometimes there's a lot of finger-pointing about the origin of the spillage," says Carlson. "We try to figure out where it came from, but usually we just manage the stoppage."

Workers installing sewers in the early 1800s.

What's remarkable about the state of L.A's sewers is that they've managed to stay relatively intact in such a seismically active area. Obviously the pipes installed in 1885 and before have survived several earthquakes, but that doesn't mean they're invincible. The city's underground still hasn't fully recovered from the 1996 Northridge earthquake, says Carlson. "It really set us back and it really cost a lot."

And there's a looming natural disaster that might wreak havoc on the sewer system, although much more slowly: the drought. If trees aren't getting the moisture they need, they'll grow roots lower into the soil to try to find water, which can interfere with drains and pipes.

As close as I'd get to full-immersion. The older tile and cement lines are gradually being replaced with these plastic shells made in the Middle East.

But the most frequent problem is not a catastrophic collapse of infrastructure—rather, it's what people put down the sewers, not realizing that it has a detrimental effect. Most people don't consider that everything in a sewer that isn't human-generated or paper needs to be removed and transported to a landfill.

"The more things that are put down it, the more manpower and energy it takes to extract it," says Carlson. In fact there's one thing in particular he would like to tell Angelenos to stop flushing: "The big thing we notice is these disposable wipes. They don't break down. Sometimes we pull out these rag masses that are like basketball-sized."

A skunkworks for stink

One of the biggest issues in managing a sewer system is the part you can't see at all: preventing odors. Not far from where I walked through a slice of old sewer is a neighborhood on the LA River called Frogtown, where Carlson's team has set up a laboratory for testing how sewer flow makes its way through pipes and drains while emitting the least amount of stench possible.

There's a difference between inconvenient stink and dangerous stink. When Carlson has to send workers below ground, they have to test to make sure the air is safe to breathe. "We put in what we call a "sniffer"—an atmosphere tester that will test for low oxygen, hydrogen sulfite, and other dangerous gases," he says. "If everything's okay we'll hoist them down."

Giant tubes of all shapes and sizes are designed for hydrological experiments.

But here, it's just the innocent smells that come wafting up from the sidewalk on a hot summer day that they're attempting to curb. What hydrologists and other engineers are trying to study is how to direct the "flow" (a nice way to say pee and poo) in a way that will keep it moving swiftly but also diminish its scent. So they build these massive prototypes of drains and pipes using their knowledge of fluid mechanics to ensure that the sewage isn't being jostled around too much—that agitation is what creates the unsavory smells.

Testing tubes looking like a giant habitat for gerbils and a cartoonish pipe organ.

Here they can experiment with materials as well as the design of pipes to find out what works best to stifle smells. Clay pipes with rubber gaskets are still the winners for most parts of the city, although PVC needs to be used in sandy, coastal soils that are prone to shifting. Concrete, while durable, can be compromised by hydrogen sulfite gas (the stuff that smells like rotten eggs).

I wandered the workshop in awe. Sheltered under the corrugated plastic roof are massive Rube Goldberg-like contraptions cobbled together from scraps of wood and sawhorses, some of them two stories tall. The clear Plexiglass cylinders sprawling through the space makes it feel like a pneumatic tube system, except for the fact that some of the tanks are filled with water. On a shelf are dozens of sockets and joints, as well as a KitchenAid mixer (which apparently is great for mixing up small batches of cement). All this tinkering just to keep our cities smelling fresh.

A tangle of pipes delivering water and "flow" are ready to be accessed for simulations.

My peek under the manhole was filled with such eye-opening moments. It's tough when your job is to help keep a hulking infrastructural system as invisible as possible, and Carlson and his department don't get a whole lot of credit. "We're not LAPD, we're not LAFD, we're not LADWP, we're not trash collection. We're out of sight, out of mind, and the only time people think about us is when their toilet doesn't flush," he says. "We just keep the water moving, but a lot of people don't realize the technology it takes."

I've now gained a new appreciation for where my own "flow" goes. I find myself mentally indexing manholes and reading the spray-painted utility-identifying letters on the streets, looking for clues of the sewer line that runs beneath. Somewhere below, Carlson and his army of drain bots are making sure that my sewage experience is limited to an opt-in tour. And all I have to do is flush my toilet.

Carlson is answering your questions on Tuesday, September 2 at 4:00 p.m. EST.

Top art by Jim Cooke; all photos by Alissa Walker