I don't think even the USPS can order your bank to transfer money to them, you would have to order it. As a result, I guess that the 'take it all back' refers to adjusting pay.
Even now, at my Federal government job when someone is overpaid we issue them a "debt letter" and then reduce their pay until the account is balanced. I assume it's because of the same reg/statute that fixes the clawback to 16.7%.
It suggests that even if technically and/or legally the option exists to recover the money directly from you, it's not part of the procedures that govern this type of thing (...as of today. It may have been in the past. Indeed, these procedures may well have been drawn up pursuant to the event discussed in TFA).