chemical toilet vs flush toilet

chemical toilet

noun
  • A toilet or chamber pot which treats waste in place with chemical disinfectants and deodorizers, as in airplane lavatories. 

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