cesspool vs flush toilet

cesspool

noun
  • An underground pit where sewage is held. 

  • A filthy place. 

flush toilet

noun
  • A toilet that uses water to flush urine and feces through a pipe to another location, typically a sewer main in urban settings or a septic tank elsewhere. 

How often have the words cesspool and flush toilet occurred in a corpus of books? (source: Google Ngram Viewer )