My setup is sheepmetal tubing(bent) 25cm diameter intake pipe, and an illuminum 15cm tube for outtake. Im using that EXACT idea that Zandor there made. Of course the length of it would depend on where you are putting your intake/outtake pipes.

Filter
5lb Charcoal
Filter
5lb Charcoal
Filter
5lb Charcoal
Filter

I am lucky with my filter though, my basement window comes out below my deck in my condominums and it flows right underneath neighbors deck and out into the sweet fresh air.