act
Pull.
You want the same pressure on both sides of the carbon so that the air gets evenly filtered.
Pushing through the filter causes high pressure on one side and low on the other, which isn't optimal.
Bernoulli, like the other guy said.
actually that is optimal because high pressure goes to low pressure naturally so it actually just reduces the overall resistance of the filter and causes the air to be forced out, i find it uses the filter more evenly but your fans die alot faster, and good fans are expensive, filters are cheap..
buuuut
basically, you need a pre dust filter. you can take the pre filter cit it and place it inside your scrubber, works fine. if your going to be pushing though, you want to use a centrifugal fan or anything static pressure, buuuuut it will wear the bearings aster still as it causes it to get hotter. when it comes to filtration i find it makes no difference, but pulling through the fans you really wanna be able to swap ends around so you can pullt hrough the otherside. the airflow over the filter isnt even. theres always lower pressure at one end than at the other.
I do both, i have an isolation box for my filter. my a/.c vents into the box where the filter is hanging attached to an isolationbox fan that sticks through the box (its styrofoam, high density stuff they use to make coolrooms) so im pushing and pulling through my filter, i just make sure my fan pulls harder than the a/c pushges or else the a/c dies really fast.