Fast way to wipe an external HDD?

I have recently acquired 2 new WD My Passport 4 TB external hard
drives. I really like their small size, different colors, and
the fact that they get their power from the USB 3.0 cable plugged
into the USB port on my desktop - no separate power cord and
little brick to crawl around plugging into an electrical outlet.

I have three old external hard drives that I would like to
retire. The largest is 3 TB and the smallest is 1 TB. One is an
old and slow USB 2.0. I've tried using several different free
wipe programs, but all seem to require over 15 hours to do a
one-cycle wipe on the smallest drive. I'd like quicker.

Question: Is here a good free wipe program that would wipe these
external drives in less than a workday? Once wiped, I will throw
these old drives away unless someone speaks up and will pay for
the shipping charges to get them from me to them.

Thanks in advance for your help.