A film called “Mr. Toilet: The World’s #2 Man” had better be prepared to tank at the box office. At minimum, concession sales at any theater showing Lily Zepeda ’s documentary are bound to take a plunge .

Lame bathroom jokes get old quickly, but they make good icebreakers, which makes them useful for Jack Sim, the movie’s central figure, who travels the world broaching a taboo subject. As the founder of the World Toilet Organization , “the other” W.T.O., this Singaporean activist encourages communities to build toilets, a product that almost half the world lacks access to, Sim says in the movie. Impoverished pockets of India and China are particularly underserved, and the dangers go beyond unsanitariness and pollution. (Relieving themselves in open spaces, women in India are vulnerable to rape.) The film shows how expanding toilet usage requires not simply supplying financing, but also changing habits.