You know that flash drive full of kitten pictures you carry at all times? Of course you do: we all have one. Sometimes you want to free up some space on your kitten drive, so you drag a couple gigs of old pictures to the Trash on your Mac.

But you don’t see any more free space is gained. What gives?

Well, the files are still in your Trash. You might think there’s a single “Trash” folder on your Mac, but that’s not the case: there’s one for every drive you use. The operating system presents all these as one Trash folder on your dock, but the files themselves can be found in a hidden folder in the root directory of every drive called .Trashes. You can’t see this folder unless set your Mac to view hidden folders, or plug your external drive into a Windows machine.

So how does one go about deleting the files in the Trash on an external drive? There are two main methods.

Option One: Empty Your Trash (All of It)

The simplest method: simply empty your Trash with the flash drive connected. This will delete all of the files in all of your .Trashes folders, including those on your currently connected external drives.

Right click the trash can on your dock, then click “Empty Trash.” This might take a while, but you’ll have all of your free space once it’s done.

Option Two: Use Curb to Empty Only One Drive’s Trash

If you’d rather not empty the drive on your primary hard drive, the free application Curb allows you to empty the Trash on a single drive. To get started, download the application, open the ZIP file, then drag the app itself to your Applications folder.

Launch the program and you’ll see a single window.

Drag the icon for your external drives from Finder to this window and the .Trashes folder will be deleted from.

You can optionally set the application to move junk files from your flash drive to your primacy drive. Click the gear at bottom-left to bring up the preferences window.

Check the “Move it to local Trash” and deleted files will be moved to the Trash folder on your Mac, allowing you to save space without permanently deleting the files.