Learn Italian: Il contenitore verde, lo svuotano il martedì. - The green container, they empty it on Tuesday.

This is the classic left dislocation structure you are learning. Because the direct object (il contenitore verde) was moved to the very front of the sentence to make it the main topic, Italian requires a matching clitic pronoun (lo) right before the verb to point back to it.

Why is there an il in front of martedì? Does it literally mean 'the Tuesday'?

Adding a definite article like il before a day of the week changes the meaning to indicate a recurring event. Instead of just 'on Tuesday', il martedì translates to 'on Tuesdays' or 'every Tuesday'.

Who is the subject of svuotano?

The subject is an implied 'they' (loro), shown by the -ano ending of the verb. Just like in English when we say 'they collect the trash', Italian uses the third-person plural here to talk about an unspecified group of people (like sanitation workers) doing a routine job.

Is the comma after verde grammatically required?

Yes, in written Italian, a comma is generally required in left-dislocated sentences. It separates the emphasized fronted topic (Il contenitore verde) from the main clause (lo svuotano il martedì) and reflects the natural pause you make when speaking.