Saya menuang jus dingin ke dalam termos kecil, tetapi adik saya tetap minum dengan sedotan.

Menuang is the active verb form, built from the root tuang (to pour).

In Indonesian, many everyday verbs appear with the meN- prefix when the subject is actively doing the action:

• tuang = pouring / pour (root form)
• menuang = to pour

So in Saya menuang jus dingin..., the sentence is saying I pour / poured cold juice... in a normal active-sentence pattern.

In Indonesian, adjectives usually come after the noun they describe.

So:

• jus dingin = cold juice
• termos kecil = small thermos

This is the normal pattern:

• noun + adjective

Examples:

• air panas = hot water
• rumah besar = big house
• kopi manis = sweet coffee

Ke means to or toward, while ke dalam means into.

So:

• ke termos kecil would sound more like to the small thermos
• ke dalam termos kecil clearly means into the small thermos

Because pouring involves movement into the inside of a container, ke dalam is very natural here.

Not in this sentence.

• ke dalam shows movement: into
• di dalam shows location: inside
• dalam by itself often means in / inside / within, but without the same clear movement sense

Since the juice is being poured into the thermos, ke dalam is the best choice.

Termos means a thermos, vacuum flask, or sometimes an insulated bottle/container, depending on context.

So termos kecil means a small thermos or a small insulated flask.

Tetapi means but.

• tetapi = more formal or neutral
• tapi = shorter, more casual

Both are very common, and both would work in many situations.
So this sentence could also be:

Saya menuang jus dingin ke dalam termos kecil, tapi adik saya tetap minum dengan sedotan.

That would sound a bit more conversational.

Tetap means still, nevertheless, or all the same, depending on context.

In this sentence, it shows contrast:

...tetapi adik saya tetap minum dengan sedotan.
= ...but my younger sibling still drank with a straw.

It suggests that even though the juice was poured into a small thermos, the younger sibling continued to drink using a straw anyway.

So tetap adds the sense of despite that or even so.

It can mean either one.

Adik means younger sibling. It does not specify gender.

So adik saya could mean:

• my younger brother
• my younger sister
• my younger sibling

If the speaker wants to be specific, Indonesian can use:

• adik laki-laki saya = my younger brother
• adik perempuan saya = my younger sister

Because adik saya means my younger sibling.

The first saya is the subject I:

• Saya menuang... = I poured...

The second saya is possessive:

• adik saya = my younger sibling

Indonesian often uses the same word saya for:

• I
• me
• my (in phrases like buku saya = my book)

So the repetition is perfectly normal.

The object is understood from context.

Minum means to drink. Indonesian often leaves out an object if it is already obvious.

Here, the listener can easily infer that the younger sibling is drinking the juice.

So:

• adik saya tetap minum dengan sedotan
  literally: my younger sibling still drank with a straw

It does not have to explicitly say jus itu or jusnya unless the speaker wants to emphasize it.

A fuller version could be:

• ...tetapi adik saya tetap minum jus itu dengan sedotan.

But the shorter version sounds natural.

Dengan means with or using, and sedotan means straw.

So minum dengan sedotan means:

• drink with a straw
• drink using a straw

Here dengan marks the instrument or means used to do the action.

Other examples:

• menulis dengan pensil = write with a pencil
• makan dengan tangan = eat with the hands / by hand

It is very natural and usually preferred here because the sentence joins two clauses:

• Saya menuang jus dingin ke dalam termos kecil
• tetapi adik saya tetap minum dengan sedotan

The comma helps show the pause before but.
In informal writing, some people may omit punctuation, but in standard writing the comma is a good choice.

Indonesian verbs do not change form for tense the way English verbs do.

So menuang and minum by themselves do not tell you whether the action is present or past. The time usually comes from context.

Depending on context, this sentence could mean:

• I pour cold juice into a small thermos, but my younger sibling still drinks with a straw.
• I poured cold juice into a small thermos, but my younger sibling still drank with a straw.

If the speaker wants to make the time clearer, they can add time words such as:

• tadi = earlier
• kemarin = yesterday
• sekarang = now

Usually sedotan means a drinking straw. In everyday use, that is by far the most common meaning.

It comes from the idea of sucking or drawing in, but in normal conversation, learners should understand sedotan as straw unless context clearly suggests something else.

Yes. Dingin literally means cold, but in natural translation it could be:

• cold juice
• chilled juice
• cool juice

The best English wording depends on context. Indonesian itself does not force a strong distinction here.