dirty laundry vs dirty washing

dirty laundry

noun
  • Used other than figuratively or idiomatically: see dirty, laundry. 

  • A clothes hamper or other container in which soiled laundry is placed. 

  • Unflattering or embarrassing facts, or questionable activities that one wants to remain secret, but which someone else may use as blackmail. 

dirty washing

noun
  • synonym of dirty laundry 

How often have the words dirty laundry and dirty washing occurred in a corpus of books? (source: Google Ngram Viewer )