Put the tractor onto the drainage pit.
Open the filler cap.
Take the drain plug out through the opening built into the ballast.
Let the tank drain, and collect the fuel in a container.
Clean the drain plug and around the drain opening.
Replace the plug with a new seal.
Check that there is no corrosion or grime. If traces of corrosion are present, replace
the tank.
Check the condition of the seals and replace them if necessary.