My gentleman friend has a terrible nasal drainage when he tilts his head forward. The drainage is yellow-green and smells terrible. I have asked him t

Both a bad odor and discoloration of the mucus can be a sign of a sinus infection. I suggest you have your friend consult with his physician. He can also start sinus rinsing with either the Sinus Rinse squeeze bottle or the neti pot. If his bad breath is caused by an infection, sinus rinsing will definitely help.