Gringo Flyer,
It is BECAUSE the exhaust is going to the fuel tank that a filter helps. Filtering the fuel before filling the tank is good but if you turn around and are blowing dirty oily exhaust in the tank you negate some of the advantage of prefiltering. For you doubters, go look at the condition of your exhaust tubing, and older fuel tanks. Trash in the tank cause more flameouts and poor running that fuel lines coming off. Besides a wire tie or fuel line clip will prevent that.
That's my opinion anway
Mmike