I pulled my fuel tank out last friday,
82 240D, its really pretty easy.

1) disconnect 3 fuel lines on the bottom of the tank, 2 of the 3 can be used to drain the contents of the tank.
1a) Disconnect the fuel sender wiring (under the first aid kit)
1b) disconnect the vacuum to the vacuum resivoir, it might go hiss =)
2) The fuel filler neck is only held in by a big rubber grommet, pull this grommet..or leave it in, it flexes a lot
3) 4 screws hold in the "front of the truck" wall (sheet metal w/ carpet covering) - pull this
4) 4 nuts hold in the tank itself, the tank can "fly" out the trunk when everything is disconnected

its really not all that bad, it took me 4hrs to get it out, play for 2hrs, and get it back in, I could now swap out tanks in 1 hr if need be (probably less...)
I almost didnt need to jack up my w123 either, the gas lines are above everything else.

a couple things to be careful for
-you WILL get diesel on you, it will NOT wash out the first time...be aware...
-its easier if you can climb in and sit in the trunk to get the tank out, bending over the trunk sux =)
- the tank holds 15 gallons, I think I refilled mine with 17 gallons when all was said and done (5gal from a portable tank and 12 from the gas station...


the only potential problems I ran p against are the OEm hose clamps, they are phillips-screwed on, my clamps were tight, dirty, tough to get a screwdriver in and I couldnt get one of them off (stripped the head...) This wasnt a critical failure (better that than bend the fuel tank tubing...) but required a closely sized piece of replacement tubing and hose clamp - if the size of replacement fuel hose (and clamp) arent "pretty close", plan on finding a pint of fuel on the ground the next morning, the size hose I used that seemed to work fit on the tank nipples tightly.

Ask questions now while I still remember how I did it =)

-John

__________________
2009 Kia Sedona
2009 Honda Odyssey EX-L
12006 Jetta Pumpe Duse
(insert Mercedes here)

Husband, Father, sometimes friend =)