Once the fuel has drained away you can open the hexagonal door in the room with the two camera consoles. Below you is a huge drop, but there is a pipe filled with fuel at the bottom to break your fall. Jump into it, but get out before the fuel starts to burn you. Then slash the circular door in the middle of the fuel tank and drop down the hole it makes. Follow the fuel pipes below until you reach a solid door with a ledge and window to the right of it.
Force jump up onto the ledge, smash the window and enter the room beyond it.
There are two consoles by the window. Wait five seconds and then press the right hand one. This will open the big door. Now leave the room through the window and go through the big door. Walk along the pipe and drop down it, flying across the fuel-filled room with lightning.