qǐng xiān jiǎnchá shuǐguǎn.

Here 请 works like please and makes the sentence more polite.

So 请先检查水管 is a polite request or instruction: Please check the water pipe(s) first.

A useful note: 请 does not always mean please. In other contexts it can mean to invite or to ask. But in this sentence, it is clearly the polite-request word.

先 means first and usually comes before the verb it modifies.

So:

• 先检查 = check first
• 先吃饭 = eat first
• 先看看 = take a look first

That is the normal word order in Mandarin:

请 + 先 + 动词 + 宾语
请 + first + verb + object

So 请先检查水管 is natural, while putting 先 after the verb would not be standard here.

Yes, but that is very normal in Chinese.

Chinese often leaves out the subject when it is obvious from context. In a request or instruction, the listener is understood automatically.

So this sentence can be understood as:

• (你)请先检查水管。
• Please check the water pipe(s) first.

In English, we usually need a subject or an understood you in commands. In Chinese, leaving it out is extremely common.

检查 means to inspect, to examine, or to check.

It is a fairly standard and practical verb, often used when checking:

• equipment
• documents
• health
• problems
• systems

In this sentence, 检查水管 means to inspect the pipe(s), probably to see whether there is a leak, blockage, damage, or some other problem.

Compared with 看看, 检查 is usually a bit more deliberate and serious.

Yes. 检查 is a transitive verb, so it can take an object directly.

Examples:

• 检查作业 = check homework
• 检查身体 = get a medical check / examine the body
• 检查机器 = inspect the machine
• 检查水管 = inspect the water pipe(s)

So 检查水管 is perfectly normal grammar.

By itself, 水管 can mean a water pipe, the water pipe, or water pipes, depending on context.

Chinese nouns usually do not show singular/plural the way English nouns do. The number is often left unstated unless it matters.

So 水管 here is best understood as a general object:

• the pipe
• the pipes
• the plumbing pipe(s)

If you want to be specific, you can add more detail:

• 这根水管 = this water pipe
• 那根水管 = that water pipe
• 这些水管 = these water pipes

Because none is needed here.

Measure words are used when you have:

• a number: 一根水管
• a demonstrative: 这根水管

But when the noun is just a direct object in a general statement, you usually do not use a measure word:

• 检查水管 ✅
• 检查这根水管 ✅
• 检查一根水管 ✅

For 水管, a common measure word is 根.

The tones are:

• 请 qǐng — 3rd tone
• 先 xiān — 1st tone
• 检 jiǎn — 3rd tone
• 查 chá — 2nd tone
• 水 shuǐ — 3rd tone
• 管 guǎn — 3rd tone

A few pronunciation points:

1. q in qǐng is like a softer ch sound made with the tongue farther forward.
2. x in xiān is a soft sound somewhat like sh, but again farther forward.
3. In 水管, because two 3rd tones come together, tone sandhi happens:
   • shuǐ guǎn is pronounced more like shuí guǎn
   • the first 3rd tone changes to a rising tone in actual speech

So the natural flow sounds roughly like:

qǐng xiān jiǎnchá shuíguǎn

It could. In fact, 请先检查一下水管 is very natural.

一下 often softens a verb and makes a request sound a bit lighter or less abrupt.

Compare:

• 请先检查水管。
  More direct, efficient, instruction-like.

• 请先检查一下水管。
  Slightly softer and more conversational.

Both are correct. The version without 一下 sounds a little more like a straightforward instruction.

It is fairly neutral, but a little on the practical/instructional side.

Because it uses:

• 请 for politeness
• 检查 for a clear, purposeful action
• no extra softeners like 一下 or 吧

it sounds like something you might hear from:

• a customer speaking politely to a repair worker
• a supervisor giving an instruction
• a written service note
• a procedural step

If you want it to sound a bit softer in conversation, you could say:

请先检查一下水管。

In standard Mandarin, that is not the normal order.

The natural order is:

• 请先检查水管。

Because 先 usually comes before the verb phrase it modifies.

Sentence-final 先 may appear in some regional speech patterns, but for standard Mandarin learning, you should use 先检查.

请先检查水管 is the natural sentence for Please check the water pipe(s) first.

If you say 先请检查水管, it sounds marked or awkward in this context, because it can suggest first, please do the act of checking... with unusual emphasis.

For normal everyday Mandarin, use:

请先检查水管。

Not in the most natural reading of this sentence.

Although 请 can mean invite in sentences like:

• 请他来。 = invite him to come

in 请先检查水管, it is functioning as a polite request marker. So the meaning is clearly please, not invite.

That depends on the situation.

• 看看 is lighter and more casual: take a look
• 检查 is more deliberate: inspect / check carefully

So:

• 请先看看水管。 = Please take a look at the pipe(s) first.
• 请先检查水管。 = Please inspect the pipe(s) first.

If you are talking about a possible repair problem, 检查 is often the better choice because it suggests a real inspection rather than just a quick glance.

Yes, you can:

请先检查水管吧。

Adding 吧 can make the tone sound softer or more suggestive, depending on context. But it can also sound slightly less direct and less like a formal instruction.

So the differences are roughly:

• 请先检查水管。 — polite, clear instruction
• 请先检查水管吧。 — softer, more conversational suggestion/request

Both are grammatical.