Empty search input field on the search results page

Make the search query disappear from the input field on the search results page after redirection

What is this, and where do I put this custom code?

add_filter("asp_print_search_query", "asp_change_print_search_query", 10, 2);

function asp_change_print_search_query($query, $search_id) {
  // Return empty string
  return '';
}