Where is it? Under the back seat? In the trunk? I've checked the trunk over pretty good, and all I see is the cover to the fuel tank (I believe) is it in the tank?

I've never been able to figure out the back seat, so I can't check there. It doesn't seem to come forward or out in anyway I can figure out. Please help!

Or is it under the car?

Please help, the E34 website has got instructions, but as to where the location of the filter is, all it says is "lift the back of the car". Which is a little ambiguous.