cistern vs flush toilet

cistern

noun
  • In a flush toilet, the container in which the water used for flushing is held; a toilet tank. 

  • The vessel surrounding the condenser in a steam engine. 

  • A cisterna. 

  • A reservoir or tank for holding water, especially for catching and holding rainwater for later use. 

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 cistern and flush toilet occurred in a corpus of books? (source: Google Ngram Viewer )