The instructor had a warning for the students of the D.C. rat academy: Don’t tell onlookers what you’re up to.

“We don’t want anyone saying, ‘Wow, there’s a whole academy and they are standing at the front door of this property,’ ” said Bobby Corrigan, an urban rodentologist leading the class. “You are just doing a survey. The word ‘rat’? I rather you not drop the word ‘rat.’ ”

On a recent summer afternoon in Adams Morgan, about 30 property managers, private exterminators and local government employees filled a dimly lit basement conference room at the Line Hotel to train as soldiers in the District’s never-ending war on rodents. Soon they would enter enemy territory: an alley, a tiny park and a row of restaurants.

The annual two-day rat academy came as rodent complaints reach record highs in the District. The city received more than 6,000 rat complaints to its 311 service request number last year, which rose from about 5,000 in 2017.

After experimenting with dry ice and solar trash cans, city officials are testing sterilization as the newest weapon in their arsenal. It’s been tried elsewhere, including New York City, with some success.

At the rat academy, students sat through presentations featuring how to spot signs of infestation and obtaining permits for applying pesticides.

Gerard Brown, who leads the rat control division of the D.C. health department, said he ­relocated the rat academy from downtown to Adams Morgan so students can gain practical experience on the front line.

The neighborhood has a bustling dining scene and, as a result, plentiful trash — ideal conditions for rodents.

It’s also where he grew up.

“When I was a little boy, the rats were in this alley,” said Brown, 63. “Now we’re dealing with the great-great-grandkids of those rats.”

As part of a pilot program, D.C. Health officials are trying to stop the next generation by placing bait boxes in nine locations across the city that contain a compound designed to interfere with ovulation in female rats and with sperm production in male rats. The bait is a sweet, fatty liquid that appeals to rodents.

“You know how the food is so good you lick the plate?” Brown remarked as he looked at a bait box containing sterilizing liquid in the Adams Morgan alley. “They are starting to eat the container.”

But the city lacks data on whether it’s working.

At the Adams Morgan alley, the city’s contractor for rat sterilization has installed a camera to measure the effects.

“The idea is, we don’t see baby rats,” Brown said. “If there are a lot of juveniles and babies running around, we know something is not right.”

Already, something was not right. Brown hadn’t received any photos of rats. He figured the camera must be in a bad location as he examined the contraption, which resembled a bulky walkie-talkie wrapped around a metal fence post.

It’s not like there were no rats around to say cheese.

Cases in point: The carcass caught in a nearby snap trap, the sunbaked body resting near the back door of a restaurant and a furry creature spotted hobbling under a dumpster.

“If he’s not dead, he’s dying soon,” Yaqin Upshaw, another D.C. Health inspector, remarked as he walked by.

“Come on, we’ve got to keep moving,” said Dan Coats, a Delaware-based property manager.

Coats and Upshaw were among the academy students scoping out the blocks surrounding the Line Hotel to identify factors enabling the rat population to thrive.

Those metal bowls of water left out for dogs at restaurant patios? Also a great hydration source for rats.

The cracks in the brick steps near restaurants? An easy escape path for rats.

“That bait isn’t doing anything,” Coats observed as he pointed at a bait box in an awkward position on the hotel’s landscaping.

“That’s why it’s important for people in your position to know where they should be,” replied Brown, the District’s rat czar.

Coats came to the rat academy because workers at several properties he oversees in Northwest Washington have been trying to keep rodents at bay. He has been deluged by conflicting information from pest companies and wanted to get educated.

Coats grew frustrated as he walked around Adams Morgan and spotted open dumpsters, unsealed doors and other mistakes beckoning rodents. No single entity is in charge of rat abatement for the neighborhood, where businesses hire private pest control companies to operate separately from government efforts.

“It’s a public health risk,” Coats said to Brown while they were standing in the alley.

As students filed back into the rat academy basement room, they traded notes on what they saw in the field and how they could use what they learned to limit food sources and to restrict movement for the rats of Adams Morgan.

Their instructor warned they just got a taste of the complicated battle.

“People think: Just put out a bunch of poison and kill them,” Corrigan said. “You are now trained to see what others are overlooking.”