Learn Hardcore German: Die Mülltonne vor dem Haus stinkt im Sommer manchmal furchtbar. - The trash bin in front of the house sometimes smells awful in summer.

Mülltonne is a feminine noun in German. Its gender is simply something you have to learn with the word (there is no logical reason; you just memorize die Mülltonne).

In the sentence, die Mülltonne is the subject of the verb stinkt, so it must be in the nominative case.

Feminine nominative singular definite article = die
So we get: die Mülltonne (subject, nominative singular, feminine).

Why is Mülltonne capitalized, but stinkt and furchtbar are not?

In German, all nouns are capitalized, no matter where they appear in the sentence.

Mülltonne is a noun (literally “garbage barrel/bin”), so it is capitalized.
stinkt is a verb (3rd person singular of stinken) → written in lowercase.
furchtbar is an adjective/adverb → written in lowercase.

Also, Mülltonne is a compound noun:

Müll = garbage, trash
Tonne = barrel, large bin
Together: Mülltonne = trash can / garbage bin.

Is vor dem Haus part of the subject (“the bin in front of the house”) or is it just saying where it stinks?

In this sentence it is most natural to read vor dem Haus as part of the subject phrase:

Die Mülltonne vor dem Haus = the bin in front of the house (this specific bin)
stinkt im Sommer manchmal furchtbar = stinks terribly sometimes in summer

So grammatically, vor dem Haus is attached to Mülltonne, specifying which bin we’re talking about.

If you wanted vor dem Haus to describe the place where the stinking happens, you would usually place it differently, e.g.:

Die Mülltonne stinkt vor dem Haus im Sommer manchmal furchtbar.
→ focuses more on where it stinks.

Why is it dem Haus and not das Haus or den Haus?

The basic form of the noun is das Haus (neuter). But after a preposition, the article often changes because of the case.

Here:

The preposition vor can take either dative (location) or accusative (movement).
We are talking about a fixed location (“in front of the house”), not movement towards it.

So we need the dative of das Haus:

Nominative: das Haus
Dative: dem Haus

den Haus would be wrong here. den is dative masculine singular or accusative plural, but Haus is neuter singular.

Why does vor take the dative here and not the accusative?

vor is a so‑called two‑way preposition (Wechselpräposition). These can take:

Dative when they express location (Wo? – where?)
Accusative when they express direction/movement (Wohin? – to where?)

Compare:

Die Mülltonne steht vor dem Haus.
→ Where is it? In front of the house. (location → dative: dem)
Ich stelle die Mülltonne vor das Haus.
→ Where am I putting it (to where)? In front of the house. (movement → accusative: das)

Your sentence describes a bin that is already located in front of the house, so we use vor dem Haus (dative).

What exactly is im Sommer, and why not in dem Sommer?

im is a contraction of in dem:

in (in) + dem (dative article) → im

im Sommer literally = in dem Sommer = “in (the) summer”.

In everyday German:

Im Sommer is the normal way to say “in (the) summer” in general.
In dem Sommer is possible but sounds like you are referring to a very specific summer that was just mentioned or is clearly defined, e.g.:
- In dem Sommer, als ich 10 war, waren wir in Italien.
  “In the summer when I was 10, we were in Italy.”

So in your sentence, the natural form is im Sommer.

Is the order stinkt im Sommer manchmal furchtbar fixed? Could I move manchmal or im Sommer?

The order in German adverbials is somewhat flexible, and your sentence is already correct. But you can move elements for different emphasis.

Some common variants:

Die Mülltonne vor dem Haus stinkt im Sommer manchmal furchtbar.
→ Neutral; slight focus on in summer.
Die Mülltonne vor dem Haus stinkt manchmal im Sommer furchtbar.
→ Slightly more focus on the fact that it only sometimes happens in summer.
Im Sommer stinkt die Mülltonne vor dem Haus manchmal furchtbar.
→ Strong emphasis on in summer (contrast with other seasons).
Manchmal stinkt die Mülltonne vor dem Haus im Sommer furchtbar.
→ Strong emphasis on sometimes.

All are grammatically correct; word order mainly affects focus and rhythm, not correctness.

Can manchmal go in other places, like right after the subject or at the end?

Yes. manchmal (sometimes) is quite mobile in the Mittelfeld (the middle part of the German clause). With your sentence you could say, for example:

Die Mülltonne vor dem Haus stinkt manchmal im Sommer furchtbar.
Die Mülltonne vor dem Haus stinkt im Sommer furchtbar manchmal. (possible, but the final manchmal sounds a bit awkward in everyday speech)
Manchmal stinkt die Mülltonne vor dem Haus im Sommer furchtbar.

Native speakers prefer to keep manchmal relatively close to the verb and not too far out at the end. The version in your original sentence is very natural.

Why do we use the verb stinkt instead of something like “is stinky” in German?

German has the full verb stinken, which directly means “to stink / to smell bad”. So you don’t need a construction with sein (“is”) plus an adjective:

Die Mülltonne stinkt.
= The bin stinks / smells bad.

If you want, you can also use riechen (to smell):

Die Mülltonne riecht schlecht.
= The bin smells bad.

But stinken is stronger and more vivid. Using “ist stinkig” is possible (Die Mülltonne ist stinkig), but it sounds more colloquial or childlike and is less common than simply stinkt.

Conjugation of stinken (present):

ich stinke
du stinkst
er/sie/es stinkt
wir stinken
ihr stinkt
sie/Sie stinken

What is the role of furchtbar here? Is it an adjective or an adverb, and why doesn’t it have an ending?

In this sentence, furchtbar is used as an adverb, modifying the verb stinkt:

stinkt furchtbar = stinks terribly / stinks awfully

In German, when an adjective works as an adverb (modifying a verb, an adjective, or another adverb), it generally does not take any ending. So it stays in its base form:

Er singt schön. (He sings beautifully.)
Das hat unglaublich wehgetan. (That hurt incredibly.)
Die Mülltonne stinkt furchtbar. (The bin stinks terribly.)

The same word furchtbar can also be an adjective:

Das ist ein furchtbarer Geruch. (That is a terrible smell.)
→ Here it takes an ending: furchtbar → furchtbarer because it directly modifies Geruch.

Could I replace furchtbar with other words like schrecklich or fürchterlich?

Yes. Several adjectives/adverbs can express a similar idea of “terribly/awfully”:

schrecklich – terrible(ly), awful(ly)
- Die Mülltonne stinkt schrecklich.
fürchterlich – terrible(ly), dreadful(ly) (a bit less common in everyday speech)
- Die Mülltonne stinkt fürchterlich.
sehr – very
- Die Mülltonne stinkt sehr. (weaker, just “very much”)
extrem – extremely
- Die Mülltonne stinkt extrem.

They are all grammatically fine; furchtbar, schrecklich, and fürchterlich are similar in strength and feel quite colloquial and vivid.