This original BMW power steering suction hose connects the intake line to the pump inlet.
This part is listed by BMW as BMW part number 32412282815 (32-41-2-282-815) and is described as Genuine BMW Steering Suction Hose for E60 M5 and E63/E64 M6 (2004-2010).
BMW Fitments:
5 Series
E60 / E61 (04-10) > M5
6 Series
E63 / E64 (04-10) > M6