How do I find a public bathroom?

Public bathrooms are actually against the law in New York City except if they're actually run by the city.

The city operates the bathrooms in parks. Central Park (Uptown), Bryant Park (Midtown) , Hudson River Park (Downtown West) are just a few spots where you can find a public bathroom.

Many private establishments will ask you to buy something in exchange for using the loo with a major exception. Most chain restaurants won't hassle you. Think Starbucks and McDonald's. If you see a fast food (or coffee) chain then chances are they will grant you access whether you are buying something there or not.