A new documentary explores an oddball, and oddly inspiring, corner of American capitalism. It is Bathtubs Over Broadway, an engaging trip back to the golden era of the industrial musical.

Dava Whisenant, the film’s director, received the 2018 Albert Maysles Award for Best New Documentary Director at the Tribeca Film Festival in New York. More recently in Washington, D.C., at the American Film Institute’s AFI Docs film festival, its star Steve Young, director Whisenant, and others featured in the film were on hand for a screening that was met with delight from the audience, many of whose members called Bathtubs Over Broadway the breakout hit of the festival.

Whisenant has produced a funny, emotionally moving, and unexpectedly patriotic film. Bathtubs Over Broadway centers on Young, a comedy writer and veteran of Late Night with David Letterman. Young was in charge of a segment called “Dave’s Record Collection,” in which host Letterman played snippets from kitschy, bargain-bin records: William Shatner singing, zany medical advice, a rare recording of the exuberant singing of the 1969 New York Mets.

“I was the one finding the strange records,” Young says in the film. In the Q and A after the screening, he tried to explain the appeal they exerted over him. “I didn’t really understand at first,” he said, “but I would find myself singing these songs to myself days or weeks later and thinking, ‘Why is this song about diesel engines so catchy? Why am I still wandering around singing about my insurance man?’”

What Young discovered was the lost world of the industrial musical. In the economic prosperity of postwar America, corporations paid professional composers and performers top dollar to write and stage lavish musicals just for their officers, their stockholders, and their employees to attend during trade shows. From the 1950s all the way up to the late 1980s (and as the film notes, there are still a few here and there today), performers entertained corporate audiences with shows filled with toe-tapping numbers like “Lipton’s on the Move,” “My Bathroom is a Private Kind of Place,” and “Everything’s Coming Up Citgo.”

The idea was to fire up a company’s sales force. The go-get-’em enthusiasm was mixed, too, with impertinent in-jokes griping about management. There were also some Franklinesque lines promoting good business ethics, in a song performed for Coca Cola bottlers in 1961:  “Should we make a killing today, and throw the future away, or look for the long view of the trade?” Young collected memorabilia from the era in a book he coauthored with artist, writer, and musician Sport Murphy in 2013, entitled Everything’s Coming Up Profits: The Golden Age of Industrial Musicals.

The composers and lyricists who got commissioned for this work were A-list talent. Tony Award-winners like Sheldon Harnick and Jerry Bock, best known for Fiddler on the Roof, gave the world Ford-i-fy Your Future, which they created in 1959 for Ford’s tractor and implement division. Another industrial was staged by John Kander and Fred Ebb, who wrote the songs for Cabaret. Chita Rivera, Martin Short, and Florence Henderson performed in these shows. One 1956 production cost $3 million, considerably more than that same year’s My Fair Lady, which had a budget of $446,000.

Bathtubs Over Broadway begins as a snarky joke at the expense of a square, bygone America—after all, Young’s discovery began with David Letterman, the gap-toothed king of irony. But something amazing happens about halfway through the documentary: it turns into something  surprisingly sincere and uplifting. Young’s obsession with collecting the records leads him on a detective search for the talent behind the industrials. He travels around the country meeting some of the performers and composers. They include composer Hank Bebee, actor Peter Shawn, and Patt Stanton Gjonola and Sandra Geller, two women who performed in the shows and who attended the American Film Institute screening of Bathtubs Over Broadway.

We watch as the writer becomes immersed in his research at the same time, 2014, that his job gets eliminated when Letterman decides to retire from television. “I had to find a job after having the same job for 25 years,” he says. A directionless Young finds himself taking solace in the un-ironic sunniness of the industrials. “The process of doing this made me a better person,” he told me. “It made it easier for me to connect with people in ways that I didn’t before.”

Bathtubs Over Broadway moves from camp and irony to depicting what became a second family for Young; and what began as a joke winds up saving a man in a mid-life crisis. He begins to appreciate that, as the film reminds us, Americans in the mid-20th century endured the Great Depression and World War II, and after these trials they were happy to have stable, lifelong jobs. They took pride in their work. Suddenly the cheering audiences in the vintage clips about toilets and Big Macs don’t seem like unhip dupes, but human beings who had good reason to love the companies that enabled them to advance up the economic scale from humble beginnings and achieve the American dream.

As Young, a soft-spoken man, told me after the screening, he began to really love these people. He grew particularly close to Sid Siegel. Siegel, who died in 2015, was the composer behind a show presented by American Standard in 1969. It was “The Bathrooms Are Coming,” a celebration of the all-American magic of bathroom fixtures. Young considers the resulting album, also called The Bathrooms Are Coming, “the crown jewel of my collection.”

The song “My Bathroom” is performed by Ms. Gjonola. At the AFI screening, she spoke to me about what a great experience the industrials were for young performers. The pay was generous and “you really learned how to enunciate words. Because if you didn’t say the name of the product clearly, you couldn’t sell it.” Her friend and co-star Ms. Geller noted that the jobs were perfect for her as a new mother. “Doing the show would only take up about two of four weeks,” she said. “Then you would be off for a few weeks, which allowed you to be with your family.” Asked about seeing herself in the old clips, Geller expressed pride. “It was an optimistic time in America,” she said.

Undertaken as an exercise in mockery of a forgotten subculture of bourgeois America, Bathtubs Over Broadway is by its end a tribute to American inventiveness, resiliency, and the work ethic. And yes, many of the songs do stick in your head after the credits roll.