I would imagine the pump is sitting down in the fuel regardless of how much fuel is in the tank (it wont work well otherwise!), so I guess it's just a matter of degree - how much of the pump will be dripping fuel when you remove it.

Done this on a Golf but never on a Beemer... tank was about half full and as others have said - it's messy but do-able.

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Wayne
2005 BMW X5 3.0d (b 02/05)
2001 BMW F650GS Dakar (b 06/01)