Once it starts trurning brown, it's time to take it out and change it. If you feed heavily or have a heavy fish load, they should probably be changed daily as anything that gets trapped in them is keeping the crud that produces nitrates IN your tank.
They cause more harm than good if not changed frequently enough.
As far as cleaning them...Slama told me to wash, rinse them in hot water using 1/2 cup bleach & add 1/2 cup baking powder for the rinse.
I usually air dry them for a couple of days before reuse..so far so good!
I don't prerinse my washer either.
Seems like everyone has there own method. What is the best method cut and dry. I have a 120gal FOWLR and I replace the sock weekly. I never reuse them. 0 Nitrates.
Washing machine with bleach. I usually throw in my fish towels as well. And I let them go til they overflow. I have the 50 micron ones so it's two-three days.