I figured out how to delete items that are trashed. Truthfully, it's not very intuitive as you have to filter for the trashed items, select them, and then use bulk actions to delete. It would be nice if this was documented somewhere. Also, maybe "permanently delete" or some other language would make it more obvious.
Regardless, I still have problems using a filter with any Joomla caching enabled. The buttons show for the filter, but when you click on any of them the URL changes (see hidden content) to include the filter, but the contents is not filtered and the ALL box remains selected.