dumping ground vs dung heap

dumping ground

noun
  • A landfill. 

  • Any place where unwanted items are sent. 

  • A presumably polyphyletic supraspecific taxon where species of unclear affinities are placed. 

dung heap

noun
  • A mound of animal droppings for agricultural use. 

How often have the words dumping ground and dung heap occurred in a corpus of books? (source: Google Ngram Viewer )