PC PSU Fan Reversal

WARNING!
It is very dangerous to operate on the inside of your PC and especially the inside of the PSU if you do not know what you are doing. If you are not entirely confident, do not attempt this procedure.
WARNING!

I have reversed the direction of air flow through my computer case and now pump it through a filter before it goes through the case.

This is to stop the large accumulations of dust which accumulate inside the case, and more importantly inside the disc drives.

I did it by opening the PSU inside the case, unscrewing the fan, twisting it around 180 degrees and screwing it back in. The filter is a piece of gauze affixed by paperclips which are then screwed under the case screws.

The gauze is held only in paperclips so that it may be removed easily for cleaning - with the level of dust in my room, the filter gets clogged up quite quickly.

I have noticed, however, that putting a filter across the fan inhibits flow of air, causing the case to become very hot - this is caused by putting the filter across the fan, not by changing the direction of the fan. So, my quest is now for a better filter.