All you really need to do is write one pass of zeros on them. That will prevent anyone but a very dedicated adversary with expensive equipment from recovering any data, especially on TB scale drives.
Can still take hours per drive though, which is why a lot of people skip it.
I make a random 1MB chunk, then write that all over the drive, at overlapping offsets. I've been told that really clears it. On IDE-spinning-rust disks I trusted it, not sure if I should trust these modern SSD
Can still take hours per drive though, which is why a lot of people skip it.