1. $ shred -v -n6 -z /dev/sdX (-n6 is the number of passes, when left out, 3 is standard);
2. Remove the HDD cover, drill through the platters a few times with a metal drill;
3. One minute in the workshop microwave;
4. Dispose of with the electric waste.

$ sudo shred -v -n6 -z /dev/sdX (-n6 is the number of passes, when left out, 3 is standard)

or use hdparm if devices is capable of ATA Enhanced Secure Erase

Firmware abstraction, write amplification and other characteristics make flash memory potentially unreliable targets for wiping data.