any tips on cleaning out the cowl?

since I don't have the A/C hooked up yet I opened the fresh air doors on the duster a few days ago and a ton of little leaves and what not came blowing out
I stopped in at the local car wash and shoved a vacuum hose in there as far as I could and as soon as I got back up to about 80 a bunch of junk came flying out of there again

so, is there a trick to cleaning the cowl out?