RCW 82.04.066

"Engaging within this state" and "engaging within the state," when used in connection with any apportionable activity as defined in RCW 82.04.460 or selling activity taxable under RCW 82.04.250(1), 82.04.257(1), 82.04.270, or other provision of this chapter means that a person generates gross income of the business from sources within this state, such as customers or intangible property located in this state, regardless of whether the person is physically present in this state.