i've tried this too. with decent drill and bit,designed to drill through the metal it does take <30 sec.open HD and either scratch platters or drill through them will also work, but takes a bit more time
Download CyberSchrub (free trial) and set level to Gutman (35 random passes) Follow the instructions carefully and delete the disk in 35 random passes and then remove CyberScrub. It will take a while but it can run whilst you sleep
If you can find a relatively powerful magnet (electromagnetic is the best) and expose the drive to it, that'll be the end of it.
I know that on a Mac you can choose to rewrite random data over the drive up to 32 times, basically making most data unrecoverable. I would try to find something like the for a PC.
Ding! We have a winner. EM is the best way. I have this huge solenoid around here somewhere. I'm kinda partial to running the platter through the mulcher/chipper.
If your HDD ever had Top Secret information on it, one of only 2 approved ways to destroy the data... that and burning.
the urgency of this post suggests nefarious intent. anyway, i'd open the case, then smash the platters with a sledge hammer then burn them with a propane torch then run them over a large speaker magnet then pour toilet bowl cleaner on them