how to default the tax code on purchase order lines in oracle fusion

Hi,

We have a requirement to default the tax on the purchase order lines, we don't want tax to be defaulted from item or supplier.

We only have one tax code and we want Tax to be defaulted for every PO irrespective of supplier or item, in system I can see we can default the tax from the financial options but I cannot see any field in the financial options to provide the tax code.

How can we default the tax ? please assist

Regards,