siphon vs siphon off

siphon

noun
  • A bent pipe or tube with one end lower than the other, in which hydrostatic pressure exerted due to the force of gravity moves liquid from one reservoir to another. 

  • A soda siphon. 

  • A tubelike organ found in animals or elongated cell found in plants. 

verb
  • To transfer (liquid) by means of a siphon. 

  • To steal or skim off money in small amounts; to embezzle. 

siphon off

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