This is for a 99 a4 2.8 Q.

I'm making a custom intake from the throttle body all the way to the box. Also making the box. I'll be using a cone type filter.

Only real question I have is this:

I took the box out and noticed a hose connected to the bottom of the air filter box. I know there is the intake snorkel on the top to push cold air in, but what is the rubber hose for on the bottom and where does it lead too?

I was guessing it realeses gases or the intake sucks in some gases from the hose. Anyone care to share what to do with it or what it's used for?

Thanks,

 

Could you snap a picture? You have a 99 so it is not for the Secondary Air Injection. Either way, you are fine putting a cone filter at the end of the hose. Keep in mind that an intake will not give you much but sound, as the factory air box was designed very well. a K&N filter might help do everything you want to for cheaper