chuángdān búyòng jìnpào.

A useful way to read it is:

Topic/Noun + 不用 + Verb

So here:

• 床单 = bed sheet / bed sheets
• 不用 = do not need to / there is no need to
• 浸泡 = soak

The whole sentence means something like:

As for bed sheets, there is no need to soak them.

This kind of structure is very common in instructions, product labels, and household directions.

This is because of tone sandhi.

Normally, 不 is fourth tone: bù.
But when 不 comes before another fourth-tone syllable, it changes to second tone: bú.

Since 用 yòng is fourth tone, 不用 is pronounced:

búyòng

This is a very common pronunciation rule in Mandarin.

Not exactly.

• 不用 means there is no need to
• 不要 usually means don’t or must not

So:

• 床单不用浸泡 = Bed sheets do not need to be soaked
• 床单不要浸泡 would sound more like Do not soak the bed sheets

That is an important difference:

• 不用 = lack of necessity
• 不要 = prohibition or instruction not to do something

In your sentence, 不用 is softer and means soaking is unnecessary, not necessarily forbidden.

Mandarin often leaves out subjects when they are obvious from context.

In an instruction like this, the understood subject is often something like:

• 你 = you
• or a general one/people in general

So 床单不用浸泡 can be understood as:

You don’t need to soak bed sheets
or
Bed sheets do not need soaking

Chinese is very comfortable omitting words that English often has to state explicitly.

It can be either, depending on context.

Chinese nouns usually do not change form for singular vs. plural the way English nouns do. So 床单 can mean:

• a bed sheet
• bed sheets
• the bed sheet(s)

In this kind of instruction, it usually has a general meaning, so English often translates it as bed sheets or bed linen.

It is very natural to analyze 床单 as the topic.

Mandarin often uses a topic-comment structure:

• 床单 = as for bed sheets
• 不用浸泡 = there is no need to soak them

So rather than thinking only in terms of strict English-style subject-verb structure, it is often better to think:

As for bed sheets, soaking is unnecessary.

This is one reason Chinese sentences can feel compact compared with English.

浸泡 is a more specific and somewhat more formal word meaning to soak by immersing in liquid.

• 浸 suggests immersing
• 泡 can mean soak, steep, or bubble, depending on context

In everyday speech, people often just say 泡:

• 床单不用泡
• 衣服先泡一下

But in written instructions, packaging, cleaning directions, or manuals, 浸泡 sounds more precise and natural.

So:

• 浸泡 = a bit more formal/technical
• 泡 = more conversational

Yes, absolutely.

床单不用泡 is a very natural everyday way to say it. It is shorter and more colloquial.

Compared with the original:

• 床单不用浸泡 = more formal, more written, more instruction-like
• 床单不用泡 = more casual, more spoken

Both are correct.

Both can work.

• 不用 = do not need to
• 不需要 = do not need / are not required to

So you could also say:

床单不需要浸泡

That sounds slightly more formal or explicit.
不用 is shorter, very common, and especially natural in brief instructions.

So the choice is mostly about style:

• 不用 = concise, common
• 不需要 = slightly more formal or deliberate

Because this sentence is giving a general instruction, not talking about a completed action.

了 is often used for:

• completed actions
• new situations or changes of state

But here the sentence is simply stating a rule or recommendation:

Bed sheets do not need soaking.

Since it is not about something that has already happened, 了 is not needed.

It can function as both, depending on context, but most naturally it sounds like an instruction or care direction.

For example, on a laundry label or cleaning guide, 床单不用浸泡 means:

No need to soak bed sheets.

It is grammatically a statement, but in real-life use it often serves the practical purpose of telling someone what to do.