This is the cowl drain tube for many GM vehicles from 1997-2008. This is for 1997-2004 Chevrolet Corvette C5, 2005-2008 Corvette C6, and 2004-2008 Cadillac XLR vehicles. This is a black rubber tube that drains water from the cowl section on these vehicles.

GM part # 10280066

Item is number 18 in the GM diagram.