FS2002 Boeing 737-400 Questions on Fuel

Reference FS2002 Boeing 737-400.1. How do I know how much fuel is in the center fuel tank, other thanby clicking on the toolbar "aircraft-fuel"? The fuel gauges on the dash are for the left and right fuel tanks only.2. What is the purpose of the overhead switch labled "left, off, right"? Is this to switch the fuel flow, and if yes, when should this be used?3. I noted that more fuel is drawn from the left and right tanks than the center tank. The left and right tanks therefore will become empty before the center tank. Can I draw fuel from the center tank to the left or right tank so that I can read the fuel amount on the dash gauge?Thank you.Stanner