It would be nice if there were an option to wipe the file tails (also called "slack space") on a volume. For those who are unaware, the "slack space" is the unused space beyond the end of a file in the last allocated cluster for that file. Information stored in slack space can last a very long time and cannot be destroyed with the method used by "wipe free space."
For example, a typical NTFS cluster size is 4096 bytes. If a file is 15000 bytes in size, it occupies 4 x 4096-byte clusters, a total of 16384 bytes of allocated space. The 1384 extra bytes allocated may already contain information from a file that was deleted. Multiply that by tens of thousands of files and you can see why these file tails are a forensic treasure trove of data, especially since file tails survive even the most "secure" wipes of free space.