A washing machine would be a close stand in for a nuke in size and weight.
Not having a stand in could invalidate the test, because the person/agent might sneak out of the cargo box in port and get away via a method or route that would be impossible for an agent shlepping a 150 pound bulky washing machine (or nuke).
Perhaps the "washing machine" was a stand in for a centrifuge...or actually the centrifuge itself.