Dog smell coming from air ducts??? HELP!

[Carol Burns]

Tenant moved out, terrible smell of old wet dogs in the entire house.  Have repainted, removed all carpet and vinyl, kilz all sub flooring.  Still get whiffs of dog stink that I think is coming through the air ducts.  Is there an odor "bomb" we can put in the house that will go through the air ducts?  Or some kind of super Febreeze thingie we can put in air return?  Or could the smell still be coming from the walls and floor?