http://www.harborfreight.com/25-lbs-...dia-92155.html
http://www.harborfreight.com/portabl...kit-37025.html
You have to modify the sprayer a bit larger to fit the walnut shells.
ahhh here we go:
http://www.e90post.com/forums/showthread.php?t=645616
If a few people with some garage space want to try this out, I am game to do it over a weekend
EDIT - a photo of the BMW vacuum adapter is on page 2, you put the walnut nozzel in the little hole and the vacuum thing goes right on the valve