BROOKLYN COLLEGE — The appeal of setting a play in a bar is obvious, even to a teetotaler like myself. Take a bunch of unhappy people, put them in an enclosed space, give everyone a magical elixir that makes them spill their darkest secrets, and presto: you’ve got a surefire recipe for compelling drama. Or at least, that’s what I thought before the opening night of April Ranger’s “Must Wash Hands.”