drag up vs dredge up

drag up

verb
  • Used other than figuratively or idiomatically: see drag, up. 

  • To educate reluctant pupils. 

  • To remind people of something, usually unpleasant, from the past. 

dredge up

verb
  • Used other than figuratively or idiomatically: see dredge, up. 

  • To find by diligent search, especially from unsavory sources. 

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