I don't prefilter for the very reason I want the sock to catch everything. I swap out socks every couple of days. That, unlike with canisters, allows me to remove solid waste completely from the system and minimize nitrate production.
You can wash filter socks in a variety of ways. A high pressure hose works fine. So does soaking in a little bleach/water solution. Many people save a few up and wash them in the washing machine (no soak, just a little bleach). Make sure to run a rinse cycle before putting the socks in and an extra rinse cycle after. Of course, keep away from "regular" detergents.
To dissipate the chlorine from the bleach, you can air dry the socks. An extra measure of safety would be to soak them in a bucket of water with a strong dose of dechlorinator.
