If Dava Whisenant’s joyous documentary “Bathtubs Over Broadway” served only to spotlight the occluded corner of American musical history known as the “industrial musical,” it would be perfectly entertaining in its own right. But in its portrayal of one man’s unusual journey, the film has much to say about turning ironic amusement into unalloyed appreciation.

And if you don’t know what an “industrial musical” is, relax — we were never meant to see them in the first place. Starting in the 1950s, these shows were crafted to entertain and inspire the sales reps from companies like Xerox and General Electric. Expensive and elaborate, they were often performed only a few times, at conventions or sales meetings, and they mostly exist now on souvenir soundtrack recordings (of shows with names like “Diesel Dazzle” or “The Bathrooms Are Coming!”) that weren’t intended to be shared with the general public.

Complimentary refreshments and discussion follow the film.