After you try the washing method Nellie mentioned you could put it in DIRECT SUN for PARTIAL drying. Then, because it is down, I would tumble on low for the remainder of the drying time to thoroughly dry and refresh the down's loftiness (whatever the care label recommends is best). Sunlight does wonders on whites, especially yellowing armpits of t-shirts. Another trick for general whites is pre-treating stains with a paste of hydrogen peroxide, baking soda, and a tiny bit of blue Dawn worked into the stain with an old cleaning toothbrush (peroxide being the key "bleaching" ingredient, soda to activate chemical reaction and gently abrade fibers to loosen the stain, and blue Dawn as a degreaser).