This is a project I've been putting off for some time. Initially I had to research how to do this but got side-tracked until I forgot about it. A few years later as I'm organizing a lot of notes on scripting did I find what I needed for secure erasing several salvaged hard drives I need for some other upcoming projects. From a security perspective running the script is easy. The process on the other hand is a pain in the you know what. This video shows what commands are used in CMD that go with the process. The video may be short but thee project took over 6 hours to complete.
That's for only two passes of the formatting process for just one hard drive. My advice if you have any software that automates it, then use it. If not you can modify the commands and create a batch file that do this multiple HDDs connected to your system or network.