The retailers of camping gear that I mostly have bought stuff from have generally suggested you do it yourself with a good soap intended for the purpose. I have probably washed a down sleeping bag at least a dozen times, I own several. I always used a top loading machine, which is not recommended, because that is what I had access to. The only time it did not work well was with my winter sleeping bag that was rated at minus 40 degrees. There is a lot of down in that bag and the down dried out so slowly that the down started to smell a bit in the late stages of air drying it.
My oldest down bag is 54 years old, I remember when I got it. I do not recall how many times I washed that bag. But it was my only sleeping bag during my late teens and early 20s when I was doing a lot of camping.
