Set out in bight UV sun helps some discolouration and freshens...
After many yrs, I finally took mine to the BIG machine at the laundramat. I went to four different ones to find the largest, and used it for du vets and sleeping bags. Pillows too.
Nice to have large dryers to tumble them in. Feathers never seem to dry all the way for me here. I need full summer and 5 days of flipping them if I try outside. I think I used tennis balls or an old white running shoe.
Watch for your detergents. Feathers are decomposable, organic, so use the online recommendations. For synthetic, I used a combo of cascade, oxy clean powder, and detergent. The covers were yellow and it really worked to whiten them, if environmentally unhappy overkill.
Yes it cost $10+ at the laundromat, plus detergents, but so worth it and I washed everything in a single morning.morning, with three mabhines running.