Wash. Rev. Code § 20.01.125
Every dealer and commission merchant dealing in hay or straw shall obtain a certified vehicle tare weight and a certified vehicle gross weight for each load hauled and shall furnish the consignor with a copy of such certified weight ticket within seventy-two hours after taking delivery. It shall be a violation of this chapter for any licensee to transport hay or straw which has been purchased by weight without having obtained a certified weight ticket from the first licensed public weighmaster which would be encountered on the ordinary route to the destination where the hay or straw is to be unloaded. If agreed upon in writing between a dealer or commission merchant and a grower or consigner, a certified vehicle tare weight and certified vehicle gross weight may be obtained from a hay or straw processing facility with a scale approved by the director.
RCW 20.01.125