According to this article, you can securely erase a disk by following these steps:
- Perform full drive encryption with BitLocker
- Format the drive
- Encrypt the drive again.
The second encryption ensures your first encryption key - which is usually kept on the drive - is overwritten. A zealous decrypter could recover the key and decrypt your data. But with the second encryption they can only recover the second key, and, since the older data is also encrypted, they still can't read it.
I wish to hear second opinion before I rely completely on this method. I have spare SSDs I can sell on the second-hand market. Would you sell a drive that was encrypted two times to someone you don’t know?