Learn Italian: Smaltire la plastica nel bidone giusto. - Dispose of the plastic in the correct bin.

This is the jussive infinitive (infinito iussivo). It is used for general, impersonal instructions where the command isn't directed at a specific person (like "you" or "you all"), but rather to the general public. You will see this form constantly on public signs, recipes, and instruction manuals.

Is smaltire different from buttare (to throw away)?

Yes. While buttare is the everyday, casual word for tossing something in the trash, smaltire means "to dispose of" or "to process." It implies following a proper procedure or dealing with waste correctly, which is why it is the standard verb for recycling and waste management instructions. (Fun fact: smaltire is also used for "digesting" food or "sleeping off" a hangover!)

Why is giusto placed after bidone rather than before it?

Adjectives that classify or objectively distinguish one thing from another usually go after the noun. Here, bidone giusto (the correct bin) directly distinguishes it from the wrong bin. Putting it before (il giusto bidone) would sound slightly unnatural here, as preceding adjectives often carry a more subjective or figurative weight.

If this were a negative public instruction, like "Do not dispose of plastic here," how would the sentence change?