you stick the long tube into the fuel openinig, point the other end of the tube to outside container that fuel will go to, squeeze the rubber thingy and fuel should start flow - there should be instructions with siphon tool. remember bmw tank is a saddle tank, you will only empty one half of the saddle, there still will be another half left but this procedure should get you started in the right direction.
i never heard of anyone in the US ever siphoning fuel but i saw the tool in my local wal-mart, so, it is being done