Hi broncho, your Rottweiler puppy doesn't need to be washed very often. Too much washing removes the protective oils from their coats. For when they get really dirty a gentle shampoo like Aloveen (an oatmeal shampoo) is great. Generally any dirt just brushes off when dry.
Rottweilers have a double coat consisting of a fine undercoat and a courser top coat. You don't want to remove the undercoat as it helps them to regulate their temperature. Over brushing or combing will damage their coats. Rottweilers moult twice a year in summer and winter. As puppies grow they will lose their pu