In my example, the filter is slightly inclined upwards towards the OUT end, which leads to the engine driven pump, and from there to the carb. The routing (not the angle) is as per Jabiru instructions of the day. 500+ hours and 16 years operation like this. So in the filter, tank side is fuel, engine side is air. Have tried a few things to purge the air but nope. I am glad that I do have the clear filter so that I can see what is going on and see if ever anything accumulates in there, dirt, muck, debris, a possum, etc. never had anything in the filter.
I'm convinced that my occasional fluffy idle started when I changed filter brand. My records show it to be true. True as in, that's when it all began, almost right after, but I've only just realised.
I'll need to fly some more before declaring "case closed"
Or I might go back to the original spec RYCO Z14 fuel filter, but alas, they are made who knows where overseas now too. RYCO overseeing quality control these days? Who knows.
RYCO ceased the remaining half of their filter manufacturing in Melbourne in Feb 2005. Since then, everything is sourced overseas.