So I can't take S. Capitol St all the way to B lot?
Sounds like South Capitol to M Street; left on M Street to Van Street; right on Van Street to lot B (directly in front of you at that point).
You can't turn left off of South Capitol Street at N Street to get to Lot B.
Gonna try that route myself today...I have always gone down 3 blocks past N Street to the batch plant and made a U-turn to get back onto South Capitol Street going north again.