A Rottweiler's natural tail is carried hanging while at rest, and often over the back when excited. It normally has a slight curve.
A Rottweiler does not hold it's tail in a stiff position sticking straight out from the body, but it can be captured appearing to stick straight out by a camera, with the picture taken at exactly the right moment, as the tail wags back an forth
These are the Correct ways a Rottweiler keeps his tail !