The direct object is the noun, pronoun, or other noun substitute in a sentence that receives the action of the verb; it is the noun or noun phrase that is acted upon.
Tomsk-7, whose existence was classified until about 1990, is thought to
have poured and pumped about a billion curies of high-level
waste, or 20 Chernobyls' worth, into lakes in the region and into
--"Lethal Legacy," Scientific American
All sentences with transitive verbs must include a direct object.
In most sentences, the direct object must immediately follow the verb.
Wash the test tubes.[Direct object, the test tubes, immediately follows the verb.]
However, the direct object may sometimes be separated from the verb by an indirect object.
Give me the test tubes.[Indirect object, me, comes between verb and direct object.]