Go to Walmart and get some blocks of Canning Wax by Gulf. It's 3 bucks for a one pound box. It's merely Paraffin wax.
https://www.walmart.com/ip/Gulf-Wax-...RoCtwUQAvD_BwE
Melt it in a bucket of hot water (as on a crawfish burner) and then holding the duck by the head, dip it into the wax/water. When it comes out after a little sloshing around, the wax will have seeped into the feathers. Immerse the bird into a bucket of cold water and the wax will harden again. Peel layers of wax and feathers off the bird. You can reuse the wax by immersing the peeled wax in the hot water bucket.