Removing the gas tank.
 

When removing the gas tank is it necessary to empty the fuel from the tank? Is the fuel line coupling equipped with a one way valve?

No need to empty but most preferable to have minimum amount for light weight, 23 litres is very heavy. And yep, it's a one way valve.

Perfect thanks for the answer.

But you mention 23 liters and I suppose you then mean the XT660Z model, I have the XT660X.

But I guess that they all use the same coupling.