backside vs long drop

backside

noun
  • The back side of an estate: the backyard and outbuildings behind a main house, especially (UK dialect, euphemistic) an outhouse. 

  • Used other than figuratively or idiomatically: see back, side. 

  • The reverse or opposite of anything. 

  • A person's buttocks. 

adj
  • Used other than figuratively or idiomatically: see back, side. 

  • Approaching an obstacle backward 

long drop

noun
  • An outhouse; a pit latrine. 

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