Learn Hardcore German: Wir reinigen die Wohnung gründlich.

reinigen sounds a bit more formal / technical / thorough, like to clean, to sanitize, to cleanse. It’s often used for professional cleaning, machines, clothes at the dry cleaner, etc.
- Wir reinigen die Wohnung gründlich. – We clean the apartment thoroughly (very systematically, thoroughly).
putzen is the more everyday, colloquial verb for to clean, especially for homes, windows, teeth.
- Wir putzen die Wohnung. – We clean the apartment (normal household cleaning).

In many everyday contexts for a flat/house, putzen is more usual; reinigen makes it sound very thorough or somewhat more formal/professional.

What grammatical case is die Wohnung, and why is die used here?

Die Wohnung is in the accusative case, because it is the direct object of the verb reinigen – it is the thing being cleaned.

For a feminine noun like Wohnung:

Nominative (subject): die Wohnung
Accusative (direct object): die Wohnung

So the article die looks the same in both nominative and accusative for feminine nouns. Here it’s accusative because the apartment is what we are cleaning.

Why is Wohnung used instead of Haus? What’s the difference?

Wohnung = apartment / flat (a unit inside a building)
Haus = house / building

So:

Wir reinigen die Wohnung gründlich. – We thoroughly clean the apartment (not the whole building).
Wir reinigen das Haus gründlich. – We thoroughly clean the house (the whole house as a building).

A native speaker chooses Wohnung or Haus depending on what kind of home it is.

Why does gründlich come at the end of the sentence?

In a simple German main clause, the typical order is:

Subject – conjugated verb – (objects/other info) – adverbs / manner / “detail” words at the end

Here:

Wir – subject
reinigen – conjugated verb
die Wohnung – direct object
gründlich – adverb of manner (how we clean)

So gründlich (thoroughly) naturally comes after the object and ends the sentence:

Wir reinigen die Wohnung gründlich.

You could say Wir reinigen gründlich die Wohnung, but that sounds unusual and marked; the neutral, normal order is with gründlich at the end.

Is gründlich an adjective or an adverb here?

Formally, gründlich is an adjective, but in German the same form is used as an adverb.

As an adjective (before a noun):
- eine gründliche Reinigung – a thorough cleaning
As an adverb (modifying a verb, as in the sentence):
- Wir reinigen die Wohnung gründlich. – We clean the apartment thoroughly.

So in this sentence, gründlich is used adverbially (it tells us how we clean), but its form is identical to the adjective form.

How do you conjugate reinigen in the present tense?

Reinigen is a regular verb. Present tense:

ich reinige – I clean
du reinigst – you clean (singular, informal)
er / sie / es reinigt – he / she / it cleans
wir reinigen – we clean
ihr reinigt – you clean (plural, informal)
sie reinigen – they clean
Sie reinigen – you clean (formal, singular or plural)

Our sentence uses wir reinigen – we clean / we are cleaning.

Does Wir reinigen die Wohnung gründlich mean We are cleaning or We clean?

It can mean both, depending on context.

German does not usually form a separate present progressive (like English am/is/are cleaning). The simple present wir reinigen can mean:

We clean the apartment thoroughly (habit, routine)
We are cleaning the apartment thoroughly (right now)

If you want to emphasize “right now,” you can add a time expression:

Wir reinigen gerade die Wohnung gründlich. – We are cleaning the apartment thoroughly right now.

How do you say We cleaned the apartment thoroughly in the past tense?

The most common past form in spoken German is the Perfekt (present perfect):

Wir haben die Wohnung gründlich gereinigt.

Structure:

haben (conjugated): wir haben
Participle of reinigen: gereinigt

So:

Wir haben die Wohnung gründlich gereinigt. – We cleaned / have cleaned the apartment thoroughly.

Why is Wohnung capitalized but gründlich is not?

German capitalization rules:

All nouns are capitalized: Wohnung, Haus, Tisch, Auto, etc.
Adjectives and adverbs are normally not capitalized: gründlich, schön, schnell, etc.
The first word in a sentence is capitalized: here Wir.

So:

Wir – first word of the sentence
reinigen – verb (no capital)
die – article (no capital)
Wohnung – noun (capitalized)
gründlich – adverb (no capital)

Is Wir reinigen formal or informal? Does wir have anything to do with politeness?

Wir simply means we. It has nothing to do with politeness; it just indicates the first person plural.

Politeness in German is mainly marked by du/ihr vs Sie:

du reinigst – you clean (singular, informal)
ihr reinigt – you clean (plural, informal)
Sie reinigen – you clean (formal, singular or plural)

Wir reinigen is neutral in terms of politeness; it just says that we (some group including the speaker) are doing the cleaning.

How do you pronounce reinigen, Wohnung, and gründlich?

Approximate English-based guide:

reinigen – [RAI-ni-gen]
- rei = like English “rye”
- ni like “nee” (short)
- gen with a soft “g” and a schwa at the end: gən
Wohnung – [VOH-noong]
- Woh = like “voh” in English “vote” (without the t)
- nung = noong, with ng as in “sing”
gründlich – roughly [GRYND-likh]
- ü is like saying “ee” with your lips rounded; somewhere between English “ee” and “u” in “burn”, but shorter
- grün ≈ “gryn” with rounded lips
- -dlich ends with the soft ch sound as in German ich, like a soft hiss from the front of the mouth; no exact English equivalent.

For accurate pronunciation, hearing native audio is very helpful.

Could the sentence be Die Wohnung reinigen wir gründlich? Is that correct, and what changes?

Yes, Die Wohnung reinigen wir gründlich. is grammatically correct.

Wir reinigen die Wohnung gründlich. – neutral order, focus on what we (we) do.
Die Wohnung reinigen wir gründlich. – emphasizes die Wohnung (the apartment), for example in contrast to something else:

Die Küche lassen wir so, aber die Wohnung reinigen wir gründlich.
The kitchen we leave as it is, but the apartment we clean thoroughly.

So changing the order is a matter of emphasis, not correctness, as long as the conjugated verb stays in second position in a main clause (reinigen is still the second element).

Is there any reflexive form here, like uns (ourselves), that is missing?

No. In this sentence, reinigen is not reflexive.

Wir reinigen die Wohnung gründlich. – We clean the apartment thoroughly.
- Direct object: die Wohnung

A reflexive version would be something like:

Wir reinigen uns. – We clean ourselves. (different meaning)
Wir machen uns gründlich sauber. – We clean ourselves thoroughly / we clean up thoroughly.

Because the object here is die Wohnung (the apartment), not ourselves, there is no reflexive pronoun in the original sentence.