get under the car and look above the subframe on the driver side - you will see a fitting with a flat shoe shaped rubber on it, if you take off the rubber cover you will see the cone shaped vent everyone talks about. Its attached to the tank with a 2 inch rubber hose, Dont worry you can take it off without drowning in diesel as the vent is from the top of the tank.

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2012 BMW X5 (Beef + Granite suspension model)

1995 E300D - The original humming machine (consumed by Flood 2017)
2000 E320 - The evolution (consumed by flood 2017)