Remove trunk lining and undo nuts holding the tank on. From below, remove the fuel lines at the tank and push the tank grommet into the trunk area. Pull on it from the passenger side to start to remove it. I can't remember where it is on a W116 but you'll have to also remove the sending unit plug.

Fairly straightforward, I think it's mostly 17mm and 19mm for the hose connections on the bottom.

__________________
Current: 1975 450SEL, 83 300D, 88 Yugo GVX, 90 300D OM603 swap, 91 F150 4.6 4v swap, 93 190E Sportline LE 3.0L M104 swap, 93 190E Sportline LE Megasquirt, 03 Sprinter, 06 E500 4Matic wagon.