Họ không những vệ sinh mà còn khử trùng.

It is the Vietnamese pattern for not only ... but also ....

So in Họ không những vệ sinh mà còn khử trùng, the speaker is saying that they do more than just clean; they also disinfect.

The structure is:

• không những = not only
• mà còn = but also

This pattern is very common in both spoken and written Vietnamese.

In this sentence, mà is part of the fixed pattern mà còn, which works with không những.

So you should learn the whole pair together:

• không những ... mà còn ...

It links the first action to an additional, often stronger or more impressive, second action.

You usually would not translate mà by itself here. It helps build the not only ... but also ... meaning.

Here, vệ sinh is being used as a verb, meaning to clean or to sanitize / do cleaning depending on context.

Vietnamese words can often function in more than one way depending on the sentence.
For example:

• vệ sinh as a verb: Họ vệ sinh phòng học = They clean the classroom.
• vệ sinh as a noun-like word: giữ vệ sinh = maintain hygiene / cleanliness

In your sentence, it clearly acts as an action: they clean.

They are related, but not the same.

• vệ sinh = cleaning, making something clean, removing dirt
• khử trùng = disinfecting, killing germs / microbes

So the sentence suggests a progression:

1. They clean
2. They also disinfect

This makes sense in real-life contexts like hospitals, kitchens, clinics, or public facilities, where disinfecting is more thorough than just cleaning.

Vietnamese often omits the object when it is already understood from context.

So Họ không những vệ sinh mà còn khử trùng could imply:

• They not only clean the place
• They not only clean it
• They not only clean the equipment / room / area
• but also disinfect it

English usually prefers an object more often, but Vietnamese can leave it out if the listener already knows what is being talked about.

Họ usually means they or them, depending on the sentence.

In this sentence, it is the subject, so it means they:

• Họ không những vệ sinh mà còn khử trùng = They not only clean but also disinfect.

It is a neutral, common third-person plural pronoun.

Yes. That is very common.

You can say:

• Họ không chỉ vệ sinh mà còn khử trùng.

This means basically the same thing: They not only clean but also disinfect.

Both không những ... mà còn ... and không chỉ ... mà còn ... are standard.
Không chỉ is often slightly more common in everyday speech, but both are natural.

In standard, careful Vietnamese, the full pattern is usually:

• không những ... mà còn ...

However, in real speech or informal writing, people sometimes shorten things, especially if the meaning is obvious. Still, for learners, it is best to use the full structure because it sounds complete and natural.

So the safest pattern to learn is:

• không những A mà còn B

It is natural and correct, but it sounds a little neutral to formal, especially because of không những ... mà còn ... and the words vệ sinh and khử trùng.

You might hear it in:

• announcements
• advertisements
• health-related contexts
• workplace or service descriptions
• news or informational writing

In very casual speech, people might use simpler wording depending on context.

Yes, but only in certain contexts.

For example:

• đi vệ sinh = go to the toilet / bathroom

But in your sentence, vệ sinh clearly means to clean, because it is paired with khử trùng. The context is about hygiene/cleaning actions, not using the bathroom.

This is a good example of why context matters a lot in Vietnamese.

The order is very close to English once you know the pattern:

• Họ = they
• không những = not only
• vệ sinh = clean
• mà còn = but also
• khử trùng = disinfect

So the structure is:

• They + not only + clean + but also + disinfect

Vietnamese often follows a straightforward subject + verb pattern, and this sentence is a good example of that.

Yes, definitely.

For example:

• Họ không những vệ sinh phòng học mà còn khử trùng phòng học.
  • They not only clean the classroom but also disinfect the classroom.

But Vietnamese often avoids repeating the object if it is obvious. So a more natural version might be:

• Họ không những vệ sinh phòng học mà còn khử trùng nữa.

Or:

• Họ không những vệ sinh mà còn khử trùng phòng học.

Exactly how much you repeat depends on style, clarity, and context.

A rough pronunciation guide is:

• vệ sinh ≈ veh sinh
• khử trùng ≈ khuh trung

But tones matter a lot in Vietnamese:

• vệ has a heavy falling tone
• sinh is level
• khử has a dipping/creaky-type tone in Northern pronunciation
• trùng has a falling tone

If you are learning pronunciation, it is best to listen to native audio because Vietnamese tones are difficult to capture well with English spelling alone.