[ALUG] Tools to clean "empty space" on disks

Are there any tools around that can clean empty space on disks? I'm not too worried about doing this for secure deletion purposes, I just want to get a good result from a compressed image of the disk. NB: I tend to use: dd if=/dev/hdb | gzip > hdb.dd.gz .. but there's probably a much better way to do this. Usually it's an NTFS disk but in this particular case it is ext3. -- Mark Rogers // More Solutions Ltd (Peterborough Office) // 0845 45 89 555 Registered in England (0456 0902) at 13 Clarke Rd, Milton Keynes, MK1 1LG