I read this book in the mid-to-late 80's. It was a new book then as it was a gift, but I do not know how old the stories were that were collected within. It was a hardcover with compilations of SciFi or possibly SciFantasy short stories. The cover was of far away green and pink clouds with floating city within the clouds.
I do not remember the actual plot, as what I remember doesn't even make much sense. But the way in which the scene was described has stuck with me all these years.
The short story, as I remember it, involves a young boy that has to take a bath but doesn't want to. His mother tells him to go anyway. Once in the bathroom he either imagines a gigantic whale in the bathtub or that there is a gigantic whale in the bathtub. He yells to his mom that he isn't able to take the bath because of the whale.
The next part is what sticks in my mind. He then goes into incredible detail of the sights, smells, sounds, and funny absurdity of a giant whale in the tub. The incredibly descriptive details of the smell of briny saltwater, barnacles, seaweed, the eye of the whale looking at him, every detail of the smelly, salty sea, and this whale in his bathroom.
I don't remember exactly how it ends but I want to say that he runs to his mother to explain, bringing her back into the bathroom to show her. The whale is gone. Or is it? There was something tiny left in the tub or the drain...I can't remember exactly. It gave the impression that asked, was it real or the incredible imagination of this boy?