I doubt the factory installed the lead. Most likely a PO did that to keep out small critters.
If it is a drain for the system you would have to open the faucets and brake the vacuum to drain the system.
WBCCI 12156 AIR 3144 WACHUNG TAC NJ6
2004 Excursion 4x4
1991 34 ft. Excella +220,000 miles, new laminated flooring, new upholstery, new 3200 lbs axles