Often times, the smaller the car is, the more difficult maintenance can be. This holds true for the Ford Focus and its fuel tank. If you must remove the tank from the car for any reason, it takes a little more effort to disconnect all its connections (including those to the exhaust system) than it does with some other cars.
It's a good idea to use up as much of the gasoline as possible before you prepare to remove the tank. Then relieve the fuel pressure by removing the fuel pump fuse from the fuse box; it should be fuse No. 12. Now try to start the car; if it comes on, it should stall after a few seconds. Once the engine won't start, crank it for a few more seconds. When the pressure is gone, open the gas cap and disconnect the negative battery cable. Siphon out the remaining gasoline into a gas can; use a vacuum pump-based siphoning kit. Block the front wheels as a safety precaution, then raise the car's rear end and remove the rear wheels.
Remove the Tank
Disconnect the exhaust system's front end from the tank by removing the nuts for the flange behind the flexible pipe; you'll need an axle stand or other type of support for this end of the system. Remove the heat shield in the rear by removing its "flat nut" fasteners. Then unhook the mounting rubbers for the exhaust system at the front and rear; this will likely require a special tool from a parts store. You don't need to remove the rear end of the exhaust; just let it rest on the rear suspension cross member.
Disconnect the filer pipe and vent hose by loosening the hose clamp; don't use sharp tools on the clamp, or you could damage the pipe. Remove the charcoal canister at the tank's rear end by disconnecting the hoses (pull off the vapour hoses and release the fitting for the other) and depressing the metal clip so you can lift the canister up and off. Disconnect the supply and return lines from the fuel filter by releasing their fittings; you should place a container under the filter to catch any fuel that comes out.
Now raise a jack with a block of wood on it to support the tank, and unhook the tank's straps by removing the strap bolt. Gradually lower the tank and disconnect all other lines as needed; this should include the wiring plug at the top for the fuel pump and gauge sender.