Take it with a grain of salt, but my understanding is duck feet (outward turned feet) is a lack of internal rotation in the hips and the hips being pulled into external rotation. I have this slightly in both feet and have been using this technique to improve it (with good results after a couple weeks) and a few of the ones outlined in Becoming a Supple Leopard.

https://www.youtube.com/watch?v=inKpTU_TFrU

Again I am no expert by any stretch, but working on my hip internal rotation helped me.