Symbolism, Imagery, Allegory
Black uses drunks hiding a bottle as an example of how human desire drives us to do ridiculous things, in general. Check it out:
BLACK: Oh yeah. [The toilet's] a favorite place for drunks to hide a bottle. But the point of course is that the drunk's concern aint that he's goin to die from drinkin—which he is. It's that he's going to run out of whiskey fore he gets a chance to do it… (58)
A psychologist of sorts, Black explains that people often desire the thing that's bad for them, doing anything to avoid searching for the thing they really want. In his view, the thing everyone really wants is to be loved by God. All of our attempts to desire other things—knowledge, power, whatever—are ways of avoiding that real, central desire.
For the record, this hearkens back to the great Christian-Catholic thinker, Saint Augustine, who thought that our desires were always meant to reach toward God, but ended up getting redirected toward other, lesser objects.