drain away vs go back

drain away

verb
  • To diminish over time; to disappear or leak out gradually. 

go back

verb
  • To extend into past time. 

  • To return to a place or state after having been there at a previous time. 

  • To have known each other for a certain length of time. 

  • To go back on. 

How often have the words drain away and go back occurred in a corpus of books? (source: Google Ngram Viewer )