bro
how do u determine whether its dirty?
by using the fingers to determine?
lol....for me i'll use my eyes to determine lo kekekeke.
if u feel tat it is dirty then ma wash lo :D
terbalik n use lor... lolz...if upper part dirty, lower part no dirty & outer part dirty & inner part no dirty... then how...???
terbalik n use lor... lolz...
of coz wash lah.... sure on top dirty while bottom clean... if bottom also dirty means ur air filter not efficient in filtering dirt n dust...