I only use a single filter on the line from the jug to the plane. When I defuel the plane at the end of the day, it gets backwashed back into the jug. I've only had one occassion when something got flushed from a tank that blocked the needle valve. Resulted in a dead stick.

Using multiple filters is only moderately effective, as anything that gets past one filter will get past the others. Best to use one filter just prior to entry to the tank. A filter on the line between the tank and the carb might be a good idea if you're worried about contamination from the exhaust line or degradation of the fuel lines inside the tank.

Brad