Den Fleck auf dem Hemd wasche ich sofort mit Wasser aus.

German often puts the most important or most topical information first. Here, Den Fleck is moved to the front for emphasis, as if the speaker is saying That stain, I’ll wash it out immediately with water.

This does not change the basic meaning. A more neutral version would be:

Ich wasche den Fleck auf dem Hemd sofort mit Wasser aus.

Both are correct, but the original gives extra attention to the stain.

Because Fleck is the direct object of the verb auswaschen.

• der Fleck = nominative singular
• den Fleck = accusative singular

Since the sentence is about washing out the stain, the stain is what receives the action, so German uses the accusative.

Also, Fleck is a masculine noun:

• nominative: der Fleck
• accusative: den Fleck

Because German main clauses follow the verb-second rule.

In a normal sentence, the conjugated verb must come in the second position. Since Den Fleck auf dem Hemd is placed first, the verb wasche must come next, and then the subject ich comes after it.

So the structure is:

1. Den Fleck auf dem Hemd
2. wasche
3. ich
4. sofort mit Wasser aus

This is very common in German word order.

Auswaschen is a separable verb. It means to wash out or to remove by washing.

In a main clause, separable verbs split up:

• the conjugated part goes in the usual verb position: wasche
• the prefix goes to the end: aus

So:

• infinitive: auswaschen
• main clause: ich wasche ... aus

This is similar to English wash out, where out is also a kind of added particle.

Because auf is a two-way preposition:

• dative for location
• accusative for direction/movement toward something

Here, the stain is located on the shirt, so German uses the dative:

• auf dem Hemd = on the shirt

If there were movement onto the shirt, then accusative would be used:

• Ich lege das Buch auf das Hemd. = I put the book onto the shirt.

But in your sentence, nothing is moving onto the shirt. The phrase only describes where the stain is.

It most naturally describes the stain: the stain on the shirt.

So the noun phrase is:

den Fleck auf dem Hemd = the stain on the shirt

This tells us which stain is meant. It is not mainly telling us where the washing happens, but rather where the stain is located.

Mit Wasser means with water, and it tells you the means or instrument used to do the washing.

The preposition mit always takes the dative, and Wasser here is dative:

• mit Wasser = with water

This is similar to English:

• I clean it with water
• I wash it out with water

Because Wasser is being used as an uncountable material noun, like water in English.

German often leaves out the article with substances when speaking generally:

• mit Wasser = with water
• mit Seife = with soap
• mit Milch = with milk

You could add an article in some contexts, but here mit Wasser is the normal, natural choice.

Sofort is an adverb meaning immediately, and its position is quite natural here.

The sentence order is arranged roughly like this:

• topic/object first: Den Fleck auf dem Hemd
• finite verb: wasche
• subject: ich
• adverb of time: sofort
• prepositional phrase: mit Wasser
• separable prefix: aus

German adverbs can move around more than in English, but this placement sounds very normal. It puts sofort in a clear, central position.

Yes, absolutely. That is a very normal sentence.

The difference is mainly emphasis:

• Ich wasche den Fleck auf dem Hemd sofort mit Wasser aus.
  More neutral, straightforward.

• Den Fleck auf dem Hemd wasche ich sofort mit Wasser aus.
  More emphasis on the stain.

So both are correct; the original just highlights the object.

Usually, yes—at least more strongly than plain waschen.

• waschen = to wash
• auswaschen = to wash out / wash away / remove by washing

So auswaschen suggests that the goal is to get the stain out of the shirt, not just to wash the shirt in general.

Because German does not need an extra pronoun or repeated object here. The object is already clearly stated at the beginning:

Den Fleck auf dem Hemd

After that, the sentence continues with normal German word order. English sometimes uses extra repetition for emphasis, such as That stain, I’ll wash it out right away, but German usually does not need to repeat it.

So the sentence is complete and natural as it stands.