Just out of curiosity... do you really have data that is so sensitive/confidential that you need to physically destroy the drive? I ask because when it was recommended that you zero out the data you said you were too lazy to do that. Physically destroying the drive means you literally have to do something to it (like rubbing the platters in the mud as recommended above). Writing 0s on the drive is something that is done using software and requires no work from you.
My point is, why go to so much trouble to completely destroy something when in most cases a multi pass erase will do exactly what you want to do? Selling a computer without a hard drive is going to severely lessen the value of the computer and cut down on who you can sell it to. Most people don't know anything about computers, and if they see you advertise it without a hard drive, they will not look at your add.
If you do the multi pass erase there is very little people can do to retrieve that information. The average Joe won't have a clue how to do it, and most people really don't care about it. The OS will show them there is nothing on the drive, and they won't look any further. Plus a multi pass erase makes it next to impossible to retrieve the information anyway.
And so I ask again, do you really have information that it so important that you must physically destroy the drive?