i was told you could do it from the workbench by selecting some sort of 'scrap all' option from the workbench menu.
seems that was BS, and this other option seems pretty long winded tbh.
Go to the workbench and select 'transfer'. There'll be an option there to transfer all "junk" items to the workbench.
This!..
Maybe i was not descriptive ebough in my comment rumtruffle(if you were aiming at me with that comment)?
If scap items are stored in the workbenches it will automatically be scraqed on need.
You however need to scrap weapon or armor at the weapon or armor workbench.
Here I guess you could drop it on floor to scrap to but then you don't see that you get, might be smarter to sell.