Ah... it's springtime, and there's nothing closer to a Flight Surgeon's heart than the chance to discuss the germ theory of disease and the importance of washing (hands, gis, and other items)
I wash my gi and obi every day, and when I wore a hakama regularly I washed it once a week. I have also been accused of being a clean freak
but there it is. I also sweat like a pig.
I would encourage you all to wash all items on a regular basis (ie, before folks move away from you on the mat and the dog runs from your workout bag... if in doubt, ask your wife...). My belts shrank, I just buy ones up 1 or 2 sizes.
If for any of reasons 1-3 you do not wash your obi, please please please wash your hands after tying it and before training. Thanks. Also, everyone should be washing their hands before training, if the sneeze/cough/bleed/etc on them during class (excuse yourself and go wash, we all thank you for it), and for their own sake after class, especially if you will be adjusting contact lenses, going out for a snack, etc.
This public health message brought to you free of charge...