i keep whichever one's that have been in my pants all day...in the pants, lob them into the machine and they are fine.
( don't tumble dry them though!!! >.<)
One's i use at the paint/staging area, usually just throw in hot soapy water, with headbands/gloves overnight and they are beauty's when they come out...smell good too
some people bleach them to get them white again...
they are pretty tough thing's and not overly expensive to replace if one does get a bit wrecked.