in the toilet vs let down

in the toilet

prep
  • Finished; at an ignoble end. 

let down

verb
  • To disappoint; to betray or fail somebody 

  • To reduce one's level of effort. 

  • To soften in tempering. 

  • Used other than figuratively or idiomatically: see let, down. 

  • To allow to descend. 

  • To lengthen by undoing and resewing a hem. 

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