How to empty a taxonomy?
Taxonomy Manager makes that pretty easy:


  This module provides a powerful interface for managing taxonomies. A vocabulary gets displayed in a dynamic tree view, where parent terms can be expanded to list their nested child terms or can be collapsed.


Or you could do it manually:

foreach (taxonomy_vocabulary_load_multiple(FALSE) as $vocab) {
  taxonomy_vocabulary_delete($vocab-&gt;vid);
}


If you have a lot of vocabs/terms it would be better to split that up into a batch job to avoid out of memory errors.