Learn Hardcore Italian: Di quel cassonetto, ne parliamo con il vicino. - That dumpster, we’ll talk about it with the neighbor.

Ne stands in for a di + noun complement (here: di quel cassonetto) and is required when that complement is fronted/dislocated. Italian typically resumes a left-dislocated complement with a clitic:

Di quel cassonetto, ne parliamo con il vicino. Without ne, the fronted phrase sounds incomplete or marked in standard Italian.

Can I just say Parliamo di quel cassonetto con il vicino?

Yes. That’s the neutral, most common word order. The fronted version with ne adds emphasis or contrast to the topic (di quel cassonetto).

Is the comma after Di quel cassonetto necessary?

In writing, yes—it signals topicalization (a pause in speech). In speech you’d naturally pause there. Without the comma, it looks like a run-on or a different structure.

Could I front the phrase but drop ne: Di quel cassonetto, parliamo con il vicino?

Best avoid it. In standard Italian, left-dislocated complements are normally resumed by a clitic (ne here). Omitting it can sound nonstandard or like a deliberate rhetorical effect.

Where does ne go with other tenses or forms?

Before a conjugated verb: Non ne parliamo.
With compound tenses: before the auxiliary: Ne abbiamo parlato.
Attached to infinitive/gerund/imperative: parlarne, parlandone, parliamone.
With periphrastics: Ne stiamo parlando.

Can I replace con il vicino with a pronoun and say Gliene parliamo?

Yes. Gliene = gli/le (to him/her) + ne (about it): Gliene parliamo. Do not add the full indirect object again (avoid Gliene parliamo al vicino). In colloquial speech, gli often covers both him and her; in careful usage, use gli (to him) and le (to her): Gliene/Gliene parliamo.

Why di quel and not del?

Del = di + il (of the). Here you want of that, so you use the demonstrative adjective: di quel cassonetto. There’s no contraction with quel.

Why quel and not quello before cassonetto?

As an adjective, quello changes form:

quel before most consonants: quel cassonetto
quello before s+consonant or z: quello zaino
quell’ before vowels: quell’albero Quello by itself (as a pronoun) means that one.

Can I use su, riguardo a, or a proposito di instead of di?

Parlare di is the default; it pairs with ne.
Riguardo a/A riguardo a is more formal: Riguardo a quel cassonetto, ne/… (careful: ne specifically resumes di, not riguardo a).
A proposito di = speaking of: a discourse marker rather than the core complement.
Su can mean about (topics of books/essays): un libro su Roma. With parlare, di is usually better. Note: ne does not resume su.

What’s the nuance between parlare con and parlare a?

Parlare con = talk with (two-way conversation): parliamo con il vicino.
Parlare a = talk to (one-way or addressing someone): parliamo al vicino. Both exist, but con stresses reciprocity.

Can I contract con il to col here?

Yes. Col = con il and is standard: …ne parliamo col vicino. Plural: coi (= con i).

Is the fronted version more formal?

It’s not necessarily formal; it’s emphatic. You front the topic to highlight or contrast it. The in-line version (Parliamo di quel cassonetto…) is neutral and very common.

Can I use ci instead of ne (e.g., Ci parliamo)?

No. With parlare di, you need ne. Ci parliamo means we talk to each other, not we talk about it. Correct: Ne parliamo.

Does ne affect past participle agreement here?

No. With parlare di, ne marks a prepositional complement, not a direct object, so there’s no agreement issue: Ne abbiamo parlato, not parlat*o/a/i/e by agreement.

Is it okay to say Ne parliamo di quel cassonetto?

Avoid it. In standard Italian, don’t double ne with an explicit di + noun after the verb. Use either:

Ne parliamo (con il vicino).
Parliamo di quel cassonetto (con il vicino).

What exactly is a cassonetto, and are there near-synonyms?

A cassonetto is a large street dumpster. Related terms:

bidone (della spazzatura): bin, often wheeled, household or curbside.
cestino (dei rifiuti): small litter bin.
secchio: bucket.