There are no bathrooms in outer space.

That’s what the cast of “Interstellar” learned working on Christopher Nolan’s latest sci-fi epic, which premiered in New York on Monday night at the AMC Loews Lincoln Center.

“We got steel kidneys, because there was a long time between pee breaks,” said Bill Irwin, who plays the voice of the robot TARS. “In the scenes where there was a lot of water, there was a chemical toilet on stilts, but there was a line.” Irwin notes that of the actors playing astronauts in the film — including Anne Hathaway and Wes Bentley — Matthew McConaughey had the strongest bladder. “I never heard Matthew ask to go,” Irwin said.

The Paramount Pictures tentpole, with a budget of $165 million, shot in Iceland (made to look like outer space), Los Angeles and Calgary, which represented a small American town.

But the house where the movie’s central family grew up didn’t have a bathroom either. “You had to use a shitty Port-A-Potty,” said Timothee Chalamet, who plays McConaughey’s son. “It was like a 10-minute walk. My first real interaction with [Nolan] on set, we were both in urinals next to each other. I was, like, ‘Thanks for having me, buddy!’”

“I had no problems with the bathroom,” said Jessica Chastain, who is featured in the Earth-bound scenes. Before she talked to Nolan about the project, a Paramount employee flew a script to her in Ireland — where she was filming the indie “Miss Julie” — waited for her to read it, and then flew it back to Los Angeles. She then got on the phone with Nolan. “The heart of the film is about a father and a daughter,” Chastain said. “I was really moved by that story line.” The actress cried the first time she saw the movie, which deals with mortality and time travel.

The film’s plot has been so kept under wraps, Ellen Burstyn couldn’t even divulge what part she played. “If I tell you, I’ll blow the whole story for you,” Burstyn said. The seasoned actress admitted she hasn’t seen Nolan’s “Dark Knight” films (“Shhh! Don’t tell!”) but she’s a fan of “Memento.” “I’m a science buff and we got right into it,” Burstyn said. “I’m interested in the big bang theory.”

Lithgow said he had no trouble following the film the first time he saw it. “I wouldn’t say it’s confusing,” said the actor, who plays McConaughey’s father-in-law. He compared the movie to solving a difficult puzzle. “It pays off magnificently.”

Even though Irwin is only featured as a voice in the film, he said that Nolan still wanted him on set every day. Irwin explained: “This is very Chris Nolan — he said, ‘It would be cheaper, it would save me money, but I don’t want to do the voice in post-production. I want the actor in the scene.’ A stunt guy and I were strapped to the back of this machine making it move, and they erased us frame-by-frame later.”

The afterparty was held at Central Park’s Tavern on the Green, where guests stayed until after midnight.

(Pictured: Matthew McConaughey and Camila Alves at the New York premiere of “Interstellar”)