In this diagram: What I am wondering is why not use a small in-line fuel filter instead of the air filter? Does the air filter prevent water from getting through? Also on the side with the Fuel Tank Breather Valve is capping it the best? I just did a tank swap and removed the charcoal canister on my F650GS (EU tank holds more fuel). I plugged the breather valve. I have noticed on cold starts a bit of hesitation so I am planning to install some sort of a filter on it. Not sure if I'll use an inline fuel filter or air filter of some sort.