I've seen people use the water/air separators+filters for air compressors. They're polycarbonate though... and there's a warning sticker on them saying that oil will damage the poly.
Steeda's oil/air separator is the same air compressor filter that can be found at Home Depot... but Home Depots is $12 and Steedas is $60.
spmotorsports url with the Steeda for sale:
http://www.spmotorsports.com/ATCmisc_fluidseparators_oil.html Home Depots separator/filter:
http://www.homedepot.com/prel80/HDUS/EN_US/shop_cart/pg_print_product.jsp?CNTTYPE=PROD_META&CNTKEY=shop_cart%2fpg_print_product.jsp&prod_id=169654 
