Let us remember that symbolism can be related to objects but also actions and characters. The major symbolism in this story relates to how Krebs lives his life once he has returned from war and how he spends his time at his family's house. We are given quite a detailed description of how he spends his days:
During this time, it was late summer, he was sleeping late in bed, getting up to walk down to the library to get a book, eating lunch at home, reading on the front porch until he became bored and then walking down through the town to spend the hottest hours of the day in the cool dark of the pool room. He loved to play pool.
We can see that Krebs lives his days free from responsibility and involvement with others. He essentially lives an isolated life where he does what he wants to do and does not have to answer to anybody else or to "conform" to society's expectations of him and what he is expected to do and how he should be living his life. Note how, later on in the story, when refering to his lack of interest in pursuing a relationship with girls, the text tells us:
He did not want any consequences. He did not want any consequences ever again.
We can see that how he spends his time is symbolic of this inner desire within him. Having seen and endured the horrors of war, Krebs now never wishes to become involved in life to such a degree that there would be consequences. His actions symbolically show this attitude, pointing towards someone who is emotionally exhausted and desperate to avoid commitment.