Use Dban as already suggested. Couple of other steps you can take... Remove the drive from the machine and place it or parts of it in a nontransparent bag for disposal like a potato chip bag. Physically destroy the platters, most people suggest drilling through it however there is only going to be a few screws holding the drive together. Take it apart, the discs you find inside hold the data. I just put them on the belt sander for a seconds.
Dispose of the pieces piecemeal in non transparent bags.
Personally I wouldn't hand anything over to someone else unless they had an industrial shredder and I got to watch it get shredded.