Put watermelon cubes in a large pot with enough salted water to cover. Soak overnight. Drain. Cover with fresh, cold water and bring to a boil. Cook over low heat until tender. Drain. In another large pot, combine sugar, vinegar and water. Tie cloves, allspice, cinnamon and lemon in a cheesecloth bag. Add to sugar mixture and stir over medium heat until mixture boils. Boil 5 minutes. Add watermelon cubes and simmer until translucent, about 15 minutes. Remove spice bag and pack pickles in hot, sterilized jars. Refrigerate 2 weeks before using. Makes 4 quarts.