Når skraldeposen er fuld, går jeg med det samme ned med den, så lejligheden ikke lugter.

Når means when here, but specifically in the sense of whenever / when that situation happens.

In this sentence, Når skraldeposen er fuld means something like When the trash bag is full or Whenever the trash bag gets full.

A learner often compares it with:

• hvis = if
• da = when (often about a specific event in the past)
• når = when/whenever for something expected, repeated, or generally true

So når is the natural choice because this is a regular situation, not a one-time past event.

Because -en at the end makes the noun definite: the trash bag rather than a trash bag.

• en skraldepose = a trash bag
• skraldeposen = the trash bag

Danish usually adds the definite article to the end of the noun instead of putting a separate word in front, as English does.

So:

• pose = bag
• posen = the bag

The same thing happens with lejligheden:

• en lejlighed = an apartment
• lejligheden = the apartment

Skrald means trash / garbage, and pose means bag. So skraldepose is literally trash bag or garbage bag.

This is a compound noun, which is very common in Danish. Danish often joins words together into one word where English uses two.

So:

• skrald = trash
• pose = bag
• skraldepose = trash bag

The -e- in the middle is just a linking sound that appears in many compounds.

Both can relate to the idea of being full, but fuld is the most natural word here.

• fuld = full
• fyldt = filled

With containers, bags, glasses, rooms, etc., Danish often uses fuld to describe their state:

• Tasken er fuld = The bag is full
• Glasset er fuldt = The glass is full

Fyldt is possible in some contexts, but it focuses more on the idea of having been filled. In this sentence, the important point is the bag has reached capacity, so fuld fits best.

Because the sentence begins with a subordinate clause: Når skraldeposen er fuld.

After a fronted element like that, Danish main clauses still follow the verb-second rule. That means the finite verb comes before the subject in the main clause.

So the structure is:

• Når skraldeposen er fuld, går jeg ...

Not:

• Når skraldeposen er fuld, jeg går ...

This is very common in Danish:

• I morgen går jeg hjem.
• Når han kommer, spiser vi.

The finite verb in the main clause must come early, in second position.

Med det samme is an idiomatic expression meaning immediately, right away, or at once.

So:

• går jeg med det samme ned med den = I take it down immediately

Even though it is made of ordinary words:

• med = with
• det = it/that/the
• samme = same

you should learn med det samme as a fixed phrase.

Yes, literally it is close to go down with it, but in natural English the meaning is more like take it downstairs / take it down.

This is a very Danish way of speaking. Danish often uses motion verbs plus direction words:

• gå ned = go down
• gå op = go up
• gå ud = go out

When you add med den, it means you are going down with it.

So går jeg ... ned med den means that the speaker physically takes the trash bag downstairs, presumably to the trash container.

In many contexts, English would choose take rather than go with.

Because skraldepose is a common gender noun in Danish.

Danish nouns are usually either:

• common gender → take en and later den
• neuter gender → take et and later det

Since it is:

• en skraldepose

the matching pronoun is:

• den

So den refers back to skraldeposen.

If the noun were neuter, you would use det instead.

Here så means so that.

The part så lejligheden ikke lugter explains the purpose or intended result:

• so that the apartment doesn’t smell

This is not the same as så meaning then or so in conversation.

Compare:

• Jeg skynder mig, så jeg ikke kommer for sent.
  = I hurry so that I won’t be late.

So in your sentence, så introduces a clause about why the speaker takes the trash bag down immediately.

Because så lejligheden ikke lugter is a subordinate clause, and in Danish subordinate clauses, sentence adverbs like ikke usually come before the finite verb.

So:

• main clause: Jeg lugter ikke noget.
• subordinate clause: ... så lejligheden ikke lugter.

This is a very important Danish word-order pattern.

A simple way to remember it:

• main clause: verb comes before ikke
• subordinate clause: ikke comes before the verb

Danish often uses the present tense where English might also use present tense, or sometimes a more future-like meaning depending on context.

Here lugter means smells / will smell, depending on how you interpret it in English. Danish does not need a special future form here.

So:

• så lejligheden ikke lugter
  literally: so the apartment doesn’t smell

But in natural English, depending on context, you might understand it as:

• so the apartment doesn’t start to smell
• so the apartment won’t smell

The Danish present tense works fine for this general consequence.

Not directly in the same structure.

You can say:

• ... så lejligheden ikke lugter
  = ... so that the apartment doesn’t smell

But for at is followed by an infinitive structure, not a full finite clause in the same way.

A related alternative would be something like:

• ... for at lejligheden ikke skal lugte

That is grammatical, but it is a different construction and feels slightly different in tone. The original så lejligheden ikke lugter is very natural and straightforward.

Yes, in standard Danish punctuation, a subordinate clause like Når skraldeposen er fuld is separated from the main clause with a comma.

So:

• Når skraldeposen er fuld, går jeg ...

Danish uses commas more systematically around subordinate clauses than English often does.

Yes. Danish often allows small variations in wording and word order. For example, a speaker might also say something like:

• Når skraldeposen er fuld, går jeg ned med den med det samme.

This means almost the same thing. The original version places med det samme earlier, which gives slightly stronger emphasis to immediately.

So the original sentence is perfectly natural, but not the only possible way to say it.