Turns out Berta was right, and everyone else was full of...
Berta: (trying to convince Alan that his son may be constipated) I'm telling you, my youngest once ate a whole can of Play-Doh--stopped her up for two weeks!
Alan: All right, Berta.
Berta: She finally pooped out a whole ashtray.
Berta: That was the day I quit smoking.
Everyone thinks that Jake's problem is about them. Alan and Judith are convinced it is because of their divorce. Charlie and Evelyn think they have a better rapport with Jake than his parents do, but they are both too self absorbed to really connect.
Judith wants to send him to a therapist, and finally everyone else gives in. The therapist is also baffled by Jake's sullen attitude. Finally, Berta administers a dose of prune juice, and by next morning the dark clouds have lifted.
During the course of this episode it is revealed that Alan went to therapy because of his bed wetting, agoraphobia, and fear of the dark. When Charlie is skeptical of whether there was any benefit Alan says, "Hey, I can pee outside in the dark." Thus, the title.
Not the best episode, but OK. Seems like it was an endorsement of the simple folk wisdom of the housekeeper, Berta. Funny that my own mother always had the same theory whenever I was out of sorts or had a headache. And she was usually right.