When using Drush with Jenkins and GitHub, along with Lullabots tutorial for deploying Pull Requests, you may end up deploying each PR into its own database.
This Drush script provides a simple tear-down command:
drush sql-drop-database
This will drop the database for the site. Feel free to add @ aliases or @sites to drop all site DB's.
Simply checkout this repo into ~/.drush (or any of the drush locations for picking up plugins).