b. As I said, EVEN when using multiple (4-5) filters such as we do, you can STILL end up finding dirty debris, in the form of "black smudge" inside your inline filters, after xxx number of flights -(H9 makes one that can be unscrewed and cleaned, shown up above in one of my links).
I use air pressure to pump fuel from the bottle to the plane, so one felt clunk in the fill line will do.
The black sludge is fuel deposit, which will not be stopped by he filters. It is dependent of the fuel quality. In Europe, I think fuel quality is more consistent, and many additives have been added to keep fuel systems clean.
I would not use anything less than leadfree premium grade fuel, 91 octane or better. In the US, pump octane is not the same as the European Research octane. Pump octane is (MON+RON)/2. MON (motor octane number) is about 8 lower than RON (research octane). With low quality fuel the difference will even be up to 10 octane points
All European engines ZDZ, 3W and MVVS prescribe leadfree 95 Research octane (RON), which is 91 PON premium leadfree US fuel. Some people may comment that this higher octane fuel burns slower, but that is academical, and not very important in our low rpm engines. The ignition advance settings have been adapted to these higher octane fuels.