If you were not charged sales tax, you owe use tax on the items. The use tax is based on the value of the item when first possessed in Washington. As of June 1, 2002, the value subject to use tax includes any freight or shipping/handling charges paid to the seller.
To pay use tax:
§ Consumers: Complete a Consumer Use Tax Return.
§ Businesses: Report the use tax on your excise tax return.