Its hard to see, but there is a faint arrow outline on the side of the filter that shows the flow direction. Like Spare_parts stated, you want it the other way or else you won't be able to see it getting dirty. Being strictly gravity fed, and having oily 2stroke mix, a dirty fuel filter can starve your carb pretty quickly.
Your leak is likely (hopefully) coming from the thin rubber gasket on the petcock, but if you overtightened the gas tank brackets you may have a cracked at the base of a stud mount.