Learn German: Am Zoll wird verlangt, dass man den Koffer auspackt. - At customs, they demand that you unpack your suitcase.

This is an impersonal passive construction. When a general action is described without a specific doer, German often uses the dummy subject es (like Es wird verlangt - It is demanded). However, when another phrase like Am Zoll moves to the first position in the sentence, the es is completely dropped. You go straight from the first position to the conjugated verb wird.

How do we know "wird verlangt" is passive here?

The passive voice is built using a conjugated form of werden (here it is wird) plus the past participle of the main verb (verlangt). Because it is an impersonal passive, it focuses entirely on the fact that the demanding is happening, not on the customs officers who are actually doing it.

Why isn't the prefix "aus" separated in "auspackt"?

auspacken is a separable verb, so in a normal main clause, the aus would jump to the end (like Er packt den Koffer aus). But here it is inside a dass (that) clause. Subordinate clauses push the conjugated verb to the very end, which forces the prefix and the main verb back together into one single word: auspackt.

The translation says "they demand that you unpack". Why use man instead of the passive voice for the second part too?