Jeg tager skraldeposen med ud, når den er fuld.

Because tage is an irregular verb.

Its present tense is:

• jeg tager = I take
• du tager
• han/hun tager

So even though the infinitive is tage, the present-tense form is tager, not tager built in a fully regular way from the stem you might expect.

You may also hear or see tar in informal speech or writing, but tager is the standard full form.

Danish very often makes compound nouns, just like English can do in words like toothbrush or trash bag.

• skrald = trash / garbage
• pose = bag
• skraldepose = trash bag
• skraldeposen = the trash bag

The -n at the end is the definite ending, so Danish usually says the trash bag by adding the article to the end of the noun instead of putting a separate word in front.

Because Danish usually puts the definite article at the end of the noun.

Compare:

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

This is very common in Danish:

• en bil → bilen = the car
• en stol → stolen = the chair

So skraldeposen literally contains both trash bag and the.

Here med is part of the verbal expression tage ... med ud, which means something like take ... out with you / bring ... out.

So:

• tage ud = go out / take out, depending on context
• tage noget med ud = take something out with you

In this sentence, med adds the idea that you are bringing the bag along when you go outside.

In natural English, you would often simply say I take the trash bag out, even if Danish uses med ud.

Because in Danish, with verbs like this, the object often comes between the main verb and the particle/adverb.

So the structure is:

• Jeg tager
  • skraldeposen
    • med ud

This is very normal in Danish and is similar to English phrasal verbs:

• I take the trash bag out
• not usually I take out the trash bag in every context, though English allows both

In Danish, tage skraldeposen med ud sounds natural.

Yes, you often can, and it would still be understandable.

But there is a nuance:

• tage skraldeposen ud = take the trash bag out
• tage skraldeposen med ud = take the trash bag out with you / bring it out

So med emphasizes that the bag goes along with you as you head out. In everyday speech, both may occur, depending on the exact situation and the speaker’s style.

Because når is used for something that is expected to happen, especially something habitual or regular.

Here the idea is:

• when it is full = whenever it gets full / once it’s full

That is a normal, expected situation.

By contrast:

• hvis = if

So:

• når den er fuld = when it’s full
• hvis den er fuld = if it’s full

In this sentence, når fits best because filling up is expected to happen as part of a routine.

Because skraldepose is a common-gender noun, not a neuter noun.

Danish has two grammatical genders:

• en-words → referred to with den
• et-words → referred to with det

Since it is:

• en skraldepose

you refer back to it as:

• den

So:

• skraldeposen ... når den er fuld

If the noun were an et-word, you would use det instead.

Because fuld agrees with the noun it refers to.

Here it refers to skraldeposen, which is:

• singular
• definite
• common gender

For many adjectives, the basic form is used with singular en-words:

• en fuld pose = a full bag
• posen er fuld = the bag is full

You may have seen fuldt in other contexts. That form is used with et-words or sometimes adverbially:

• et fuldt glas = a full glass

But here pose is an en-word, so fuld is correct.

Because Danish often uses the present tense for:

• habits
• routines
• scheduled or expected future actions

This sentence describes a regular habit:

• I take the trash bag out when it is full

So the present tense is perfectly natural.

English does something similar in habitual sentences:

• I take it out when it’s full

Ud means out.

It usually refers to movement from inside to outside, or from an enclosed place outward.

So in this sentence it helps express the idea of taking the trash bag out.

A useful comparison is:

• ud = out, outward movement
• ude = outside, being outside

So:

• Jeg går ud = I go out
• Jeg er ude = I am outside

Here there is movement, so ud is the right form.

Yes, in standard Danish, a comma is normally used before a subordinate clause like the one introduced by når.

So:

• Jeg tager skraldeposen med ud, når den er fuld.

The part når den er fuld is a subordinate clause, and the comma marks that clearly.

This is more regular in Danish writing than in modern English, where commas before when are often omitted.

Grammatically, skraldeposen means the trash bag, so it looks definite and specific.

But in everyday Danish, a definite singular noun is often used for something that is part of a normal household routine. So the sentence naturally means something like:

• I take the trash bag out when it’s full
• in other words, whenever the trash bag gets full

So although the form is singular and definite, the meaning can still be general and habitual rather than about one single unique bag only.