Goto Finder > Help > type in Trash...
From Finder Help Trash...
" Empty the Trash
Empty the Trash without any warning or when it contains locked files
Hold down the Option key, and then choose Finder > Empty Trash "
If you have the problem where you can’t empty the Trash or eject a disk because something is preventing you? Usually the reason is because some application has a file open, and thus you can’t get rid of the disk or trash the file. Then use What’s Keeping Me!, will identify the application that is preventing you from accomplishing your task. You can then use What's Keeping Me to quit, relaunch, or kill the problem application so you can get on with your business.
Sometimes it happens that the Finder just doesn't want to empty the trash anymore and says "The operation cannot be completed because the item "" is in use.". That's a good warning if it is true, but sometimes you want to get rid of an application and this warning appears even though the only thing running is the Finder. Usually after a restart you can delete it. But that is very time consuming and even then, it is sometimes still stuck not wanting to be deleted. There is a risky command that can be used in the Terminal that will empty the trash no matter what. Risky because a simple error in the syntax could erase a lot of stuff that you want to keep.
There is a way of forcing the Finder to empty the trash no matter what! It is done in the freeware customization and maintenance application OnyX (download @ http://www.titanium.free.fr/pgs/english/apps.html ). Once you loaded OnyX and entered your administrator password, choose "Cleaning" in the top bar. Click on the "Trash" tab. You can now choose whether you want to "Delete" or to "Securely Delete" (by overwriting) and click Execute. That's it, it will force the Finder to empty the trash even if the files are in use!
Many times, depressing the Option key while emptying Trash will empty problem files. Another method – start by depressing the mouse over the Trash icon. Then empty trash from the pop-up menu. The files should be emptied.
Also look at these links.
You can't empty the Trash or move a file to the Trash in Mac OS X
Solving Trash Problems
How To Fix Stubborn Trash and Why it Won't Delete
Download Trash It! v3.6.1 from:
Download DropNuke from: