WARNING: This page is about a different car, the 2003 BMW M5, 2002 BMW M5, 2001 BMW M5, and 2000 BMW M5. However, it is still accessible from the selected car via links, so may be relevant.
FUEL TANK AND MOUNTING PARTS E39 DIESEL TECHNICAL DATA
Tank volume/reserve
ltr.
70/8
Venting: Gasoline-driven cars via rollover and bleed valve, through active carbon filter to the inlet manifold. Diesel via expansion tank into open.