You want the flank and breast feathers - if they're still on the skin I'd pull them off and wash them in dawn and borax. Let em soak up shaking them every now and then. After drain and rinse I stick in a pillowcase and put in the dryer for 5 minutes of heat then turn to just air dry.

Here's a search on duck flank feathers
https://www.google.com/search?q=duck...BTsQ_AUIrAIoAQ

Wing feathers are good for wet flies - make sure you get all the meat out of the wings. It's much nicer tying with clean feathers. Every feather can be used for something in tying.