I don't "filter", per se, but I do employ some screen mechanisms to at least make a token effort at reducing trub that makes it into the fermenter. I use a hop screen (tall, cylindrical stainless steel mesh) to contain my pellet hops during the boil, and I use a Hop Stopper (pickup tube enshrouded in a frisbee-shaped pouch of stainless steel mesh) on my kettle outlet valve to try and prevent break material from escaping out the kettle valve.