Working a midnight shift on Jan. 18, 2015, Denis Lawlor was showing a new colleague around the Metropolitan Water Reclamation District of Greater Chicago’s sprawling Stickney wastewater-treatment plant.

They were both cops — Lawlor for several years with the police department run by the government agency, which handles flood- and sewage-control for much of the Chicago region, and the colleague only recently hired.

For nearly an hour, Lawlor provided an eye-popping assessment of how things supposedly work at the district — which was all recorded after his radio handset either malfunctioned or was accidentally keyed and his remarks were somehow broadcast over an Illinois State Police radio frequency.

Among his comments, according to an audio copy:

• “Everyone here is sleeping,” Lawlor told the rookie. “The engineers, everyone that’s here on midnights, they’re all f—— sleeping somewhere, too.”

• Referring to clout hiring, Lawlor said, “Just assume everyone here is here on a phone call . . . everybody.”

• Lawlor used the “n” word, calling a black colleague a “stupid Alabama field n—–” and joking that “white guys” should call Martin Luther King Jr. Day, which was the following day, “James Earl Ray Day,” in reference to the civil rights leader’s killer.

• Lawlor used the “c” word to refer to female colleagues.

• And he discussed “the apartment” — a secret back room where he said district employees would hide out, watch TV, sleep on a couch, play cards and drink beer, stored in a refrigerator there. He’s heard telling the rookie he was welcome to grab a beer whenever: “Help yourself,” but “don’t f—— take the last one.”

Lawlor’s remarks weren’t just offensive, according to the state police, who said they also briefly tied up a critical radio frequency used by troopers, who were put at risk without that open line of communication with dispatchers.

The probationary officer Lawlor was speaking to was fired.

And, in February 2015, the water reclamation district suspended Lawlor — who’d been paid more than $100,000, including overtime, in 2014— without pay as it moved to fire him.

Lawlor has been fighting ever since to hold onto his job and, as a result, remains on the agency’s staff nearly two years after the recording, though he isn’t being paid.

Now, the reclamation district’s civil service board is expected to meet Wednesday and could rule then on Lawlor’s case, according to an agency spokeswoman.

Among the arguments Lawlor’s lawyers are making to keep his job, they say nobody can prove he ever drank or slept on the job. They say he did neither.

They also argue that, despite the water reclamation district’s allegations, the recorded conversation didn’t violate the agency’s anti-harassment and anti-discrimination policies.

“It was street vernacular,” one of Lawlor’s lawyers, Daniel Austin, said at a September civil service board hearing. “It was a private conversation . . . a union discussion.”

Austin told the board that Lawlor, who previously had been a Chicago cop, was trying “to figure out the new employee in a style that he knew from the Chicago police force.”

According to a transcript of that hearing, James Murray, a water reclamation district attorney, told the board Lawlor previously tried to explain away his remarks by saying “it was all a training exercise, and he was just trying to gauge what type of police officer the probationary officer . . . would be,” even though Lawlor “was not assigned by anybody to train him.”

Lawlor was fired from the Chicago Police Department in 1997 over an out-of-town incident in which he shot his gun while off-duty, apparently while drinking, and then “attempted to conceal his involvement” in the incident, city records show.

But his firing by the police department wasn’t found in a background check when the water reclamation district hired him in 2011.

Before the recording, Lawlor had been rated by the district as “highly effective,” according to agency personnel records, which said his performance “sets an example for others to follow.”

The government agency has about 2,000 employees, including more than 60 police officers.