All this talk of adding dirt! I have never changed a felt clunk or cleaned a fuel filter in 10 years. Not one. If your fuel has dirt in it, filter in more, if you tanks have dirt in them clean them before use (blowing glass tanks out with an airline will not clean it!)

Fuel from my MAP header tank is flushed through the inside of my felt clunks. I can count my flame outs, its a binary number...

I don't think of a felt or paper clunk/tank as a filter unit....its not.