How many plumbers does it take to fix a faulty toilet on an airplane?

None. They were all drained.

A Norwegian Air shuttle flight from Oslo to Munich was forced to turn around Saturday morning because of toilet problems, The Washington Post reported. On board were more than 80 plumbing industry workers traveling to a trade event.

The ironic circumstances led to howls of laughter among the passengers.

“Seldom has there been more laughter in an airplane ... when the reason given is ‘toilet problems,’” Frank Olsen, chief executive of the Rorkjop plumbing company told The Washington Post on Wednesday.

According to the flight data website Flightradar24, the southbound flight was heading toward Germany across the Skagerrak Strait. But 15 minutes after takeoff, the plane banked east and returned to Oslo.

The dozens of plumbers on board were unable to help out, Olsen said.

“We’d have gladly fixed the toilets, but it must unfortunately be done from the outside, and we didn’t want to take a chance on sending out a plumber at 10,000 meters altitude,” Olsen told Dagbladet, a Norwegian tabloid.

Olsen said his workers could resist toilet humor, even after their flight was rescheduled later in the day, the Post reported.

“Even the flight attendant came and told me that she have never done a U-turn with that many passengers smiling on board,” he told the Post. “We are still smiling.”