Many used westys come without the tank key. Mine came without one. Just
remove the 4 utility box screws,and pull the box away from the van. There
is enough extra water hose to do this.Disconnect the hose from the box.
Then you can take the lock apart and remove it. This is a good time to
reseal the three  boxes with silicone.Lack of a good utility box seal is
the cause of westy rust.