Does anyone know what are doing in Japan?
I think Japan people are very worried about hygiene.
This is contradictory with "to not wash" tradition.
Here in Japan I wear a yukata in the summer. Of course it has a wrap-around belt, which on occasion is washed in the washing machine, along with the yukata. This obi does not have any special sancity or significance: it simply goes with the kimono.
My current aikido training wear includes 4 keikogi (2 judo-type; 2 karate-type), 4 hakama and several obi, all except one of which are black. Two of the obi are judo-obi, I use these as spares, or on the occasions when I train without a hakama, or if I visit a dojo where the hakama is not worn. These are washed as and when necessary. The other obi are wide wrap-around obi, which I prefer to the judo style belts. These, too, are washed as and when necessary. Again, they do not have any special sanctity or significance, but simply go with everything else.
My hakama are occasionally dry-cleaned, but there are many dry-cleaners who do not know how to pleat and fold hakama correctly, so I have to subject the hapless shop owner to some interrogation before I entrust my hakama to them. The last shop I used closed and I have not yet found another.
After training, the hakama are folded up on the tatami, and put away. There is a big difference between the tatami of the dojo and the ordinary floor, of the changing room, for example. This echoes the distinction between tatami and floor area beyond the genkan in a traditional Japanese-style house. Here the uchi-soto distinction operates and people leave their shoes in the genkan, the place where hito-gomi is left behind. Equally, the floor of the dojo changing room is a 'soto' area and I rarely see anyone drop any aikido training gear on the floor.
There is some discussion of this topic in Emiko Ohnuki-Tierney's "Illness and Culture in Contemporary Japan" (Cambridge, 1984), especially Chapter 2: "Japanese Germs".