dirty laundry vs washwater

dirty laundry

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

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

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

washwater

noun
  • Water used for washing, especially in industrial processes. 

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