One thing for sure, pioneers didn't use a wash machine!LOL My grandmother had lots of down comforters, and they were hung on a line , and she used a wire thing like a tennis racket to "beat" them. This took out a lot of dead skin cells , thus removing odor, and a fresh breezy day helped too. She also used duvet type covers. At her house, we also slept on(in) featherbeds!!

Mine says to absolutely not wash . Must be dry cleaned. Had a cover made from decorator fabric. When I changed room colors I was surprised to find it marked/stained and need to clean. Seems the cat sleeping " ON " it caused stains I guess. We were sleeping under it and I never really saw the marks .
Anyway I will not try to wash as I had one very bad experience with feather pillows so never again.

I wash mine in the washer but don't agitate it. I let the washer fill with water and detergent. Turn it off and let the comforter soak. I smish it with my hands and then set the washer on spin and drain. Fill the washer with water to soak and rinse then spin and drain. I usually use the spin cycle several times and it dries fast in the dryer. I take it out of the dryer every so often to shake to distribute the filling. The decorator fabric won't fall apart in water, it's the agitation that will do it. It may bleed though.