You can use the Collection Manager to purge all objects in a given collection. This allows you to quickly delete content without having to purge objects one at a time.
Choose a collection and click the 'Manage This Collection' tab at the top.
Expand the 'Permanently Delete <Name-Of-Collection> section and the 'Are you sure?' sub-section. Click Delete This Collection to confirm the operation.
You have successfully purged all the objects in your collection.