If you've never heard of lavish musicals like The Bathrooms Are Coming or Diesel Dazzle you're not alone. Yet, these elaborate productions have borrowed the talents of some of Broadway's biggest names.

Tony-winning director Susan Stroman admits she "cut her teeth" on what was known as the industrial musical – extravagant productions the general public never got to see. Instead, they were meant for corporations to show to clients, dealers and investors.

In this April 10, 2014 file photo, director Susan Stroman attends the after party for the opening night of "Bullets Over Broadway" in New York.

Photo: Brad Barket

Now, a new documentary called Bathtubs Over Broadway allows audiences into this secret world. Stroman, along with the film's writer, director and some of its actors peeled back the curtain at the film's world premiere at the Tribeca Film Festival in New York this week.

"A lot of corporations would hire us to sing and dance about the product. And, in fact, that's how I really got started choreographing and directing," Stroman said.

Broadway legends Bob Fosse, Chita Rivera, and Sheldon Harnick also loaned their talents before making it big. And songwriting duo John Kander and Fred Ebb wrote a musical for General Electric called Go Fly a Kite before tackling shows like Chicago and Cabaret.