Слей воду из кастрюли через дуршлаг.

Слей is the informal singular imperative of слить. In this sentence it means drain off, pour off, or pour out the water.

So the basic idea is:

• слить воду = to drain/pour off the water
• слей воду = drain/pour off the water

Because слить is perfective, the command sounds like do it and complete the action.

Because вода is the direct object of the verb, and with this verb it takes the accusative case.

• nominative: вода
• accusative: воду

So:

• вода = water as the subject
• слей воду = drain the water

This is a very common pattern in Russian: the thing being acted on goes into the accusative.

The preposition из means out of / from inside, and it requires the genitive case.

• dictionary form: кастрюля = pot, saucepan
• genitive singular: кастрюли

So:

• из кастрюли = out of the pot / from the saucepan

This is the normal case pattern:

• из + genitive

The preposition через usually means through, and it takes the accusative case.

• dictionary form: дуршлаг = colander
• accusative singular: дуршлаг
  (it looks the same as the nominative because it is an inanimate masculine noun)

So:

• через дуршлаг = through the colander

In natural English, this often corresponds to using a colander.

Yes. Literally, it means through a colander. The image is that you pour the contents so the water passes through the holes while the food stays behind.

In English we might say:

• Drain the water through a colander
• Drain the pot using a colander
• Pour the water out through a colander

So the Russian is quite literal here.

Russian has no articles, so there is no direct equivalent of the or a/an.

That means:

• воду can mean the water or just water
• кастрюли can mean the pot or a pot
• дуршлаг can mean the colander or a colander

You understand which one is meant from context.

It is talking to one person informally.

• слей = singular informal command
• слейте = plural or polite command

So if you were speaking politely or to several people, you would say:

Слейте воду из кастрюли через дуршлаг.

In Russian, the subject is often left out when the verb form already makes it clear.

Because слей is an imperative, it already means you drain...! addressed to one person informally. So adding ты is usually unnecessary.

• Слей воду... = Drain the water...
• Ты слей воду... = possible, but usually more emphatic or contrastive

This is very normal in Russian commands.

Both can involve pouring liquid out, but слить is especially common for draining off liquid from something.

• слить воду = drain off the water
• вылить воду = pour the water out

In a cooking context, слить воду is usually the more natural choice when you boil something and then get rid of the water.

So with pasta, potatoes, etc., слить воду is exactly the kind of verb you expect.

Кастрюля usually means a cooking pot or saucepan.

It is not usually a frying pan. A frying pan is:

• сковорода

So:

• кастрюля = pot / saucepan
• сковорода = frying pan

In this sentence, pot is the best basic translation.

Yes, Russian word order is flexible, but this version is very natural and clear:

Слей воду из кастрюли через дуршлаг.

It presents the information in a straightforward order:

1. action — слей
2. object — воду
3. source — из кастрюли
4. method/path — через дуршлаг

You might hear other orders in real speech, but changing the order can shift emphasis or make the sentence sound less neutral.

The main stresses are:

• слей
• во́ду
• из кастрю́ли
• че́рез дуршла́г

Especially useful words to remember:

• кастрю́ля
• дуршла́г

Stress matters in Russian, so it is worth learning these with the word.

Yes. It sounds completely natural as a kitchen instruction.

It could be:

• a spoken instruction to one person
• a casual recipe-style command
• something a parent, friend, or cook says while preparing food

If a recipe wanted a more neutral or polite written tone, it might use:

• Слейте воду из кастрюли через дуршлаг.

But the original sentence is very natural in everyday speech.