beat one's meat vs flog the dolphin

beat one's meat

verb
  • To masturbate by stroking or rubbing one's penis. 

  • To waste time; to engage in an unproductive activity. 

flog the dolphin

verb
  • masturbate (male) 

How often have the words beat one's meat and flog the dolphin occurred in a corpus of books? (source: Google Ngram Viewer )