Vintage Tiger Diy Service Questions

hi all,
ive decided to give my tiger 885i a full service, as the last recent recorded one looked very dubious! and mpg has been low anyway.
so, first question. ive removed the air filter to check and it was very dirty, not in line with the so called "service" done 500 miles ago. new parts ordered, BUT, i forgot to check which way round it was fitted. i can fit it back both ways so its not obvious whether the metal mesh side should be facing forward or backwards? can anyone advise please.
next, the airbox has two rubber vent pipes coming off it. a thin rubber one and a thick plasticky one. the thick pipe has a bung fitted to the bottom to block it??? is that normal? the online parts diagram for the airbox show the pipe and something at the bottom of it (part 18) an end tip. whats the point of a drain pipe thats blocked off?
lastly, spark plugs! ive tried every tool in my kit and nothing fits down and over the plugs to remove them. i tried grinding down an old plug socket to no avail, but not even sure what size socket it should be? Also, plugs appear to be listed in diameters of the plug thread, not much help when deciding the A/F of the socket required!

any help on these matter would be greatly appreciated!