bowser vs tank wagon

bowser

noun
  • A road vehicle (often a trailer) for the transport of liquid fuel, particularly aviation fuel at an airfield. 

  • A buffoon or imbecile. 

  • A fuel metering/delivery pump at a filling station. 

  • A mobile water tank deployed to distribute fresh water in emergency situations where the normal system of piped distribution has broken down or is insufficient. 

tank wagon

noun
  • A vehicle designed to transport liquids or gases in bulk; a tanker 

  • Synonym of tank car. 

How often have the words bowser and tank wagon occurred in a corpus of books? (source: Google Ngram Viewer )