What did Martha washing tondo with all the letters George sent her?

In "The Things They Carried" by Tim O'Brien, Martha washes the letters George sent her to keep them fresh and to remove any dirt or impurities, symbolizing her attempt to preserve the emotional connection they share despite the distance and the war. This act reflects her care for George and her desire to maintain a sense of intimacy and communication amidst the chaos of conflict. The washing of the letters highlights the themes of love, memory, and the longing for connection during times of separation.