Ductography only really serves a purpose with a single discharging duct. If there are multiple discharging ducts or bilateral symptoms, the etiology is idiopathic or constitutional and ductography serves no purpose.
There is a poor correlation between the physical appearance of the discharge and the findings on ductography. The traditional impression that the "bloody" discharge is somehow more sinister is not true. Most discharges described as "bloody" are in fact dark brown on careful examination.
When performing ductography, visualization of the leaky duct can be improved by dropping a small drop of contrast onto the nipple and using it as a lens to aid visualization. Try it. It works. And with ductography as in sialography, do not use brute force and ignorance. Once you have traumatized the duct orifice your chances of success are close to zero.
Post injection, do magnified views. You see so much more.