La capa de drenaje cubre el agujero de drenaje.

In Spanish, it is very common to express this kind of idea with de + noun.

So:

• capa de drenaje = drainage layer
• agujero de drenaje = drainage hole

English often puts one noun in front of another noun as if it were an adjective, but Spanish usually does not do that. Instead, Spanish prefers a structure like:

• X de Y

So drenaje stays a noun, and de drenaje works like a descriptive phrase.

Because here drenaje is being used in a general, descriptive way, not to refer to one specific drainage system.

Compare:

• agujero de drenaje = a drainage hole / drain hole
• el agujero del drenaje = the hole of the drainage system

In your sentence, de drenaje describes the type of layer and the type of hole. It is more like a category label than a specific possession relationship.

So:

• de drenaje = descriptive
• del drenaje = of the drainage / belonging to the drainage

Cubre is the third-person singular present tense of the verb cubrir (to cover).

Conjugation in the present:

• yo cubro
• tú cubres
• él / ella / usted cubre
• nosotros cubrimos
• ustedes cubren
• ellos / ellas cubren

The subject here is la capa de drenaje, which is singular, so the verb must also be singular:

• La capa de drenaje cubre...

Because agujero de drenaje is a thing, not a person.

Spanish uses the personal a mainly with specific people (and sometimes pets or personified beings) when they are direct objects.

Examples:

• Veo a María.
• Conozco a tu hermano.

But with objects or things, you normally do not use a:

• Cubro el agujero.
• Veo la casa.

So cubre el agujero de drenaje is correct.

Normally, no. In Spanish, countable singular nouns usually need an article or another determiner.

So:

• La capa de drenaje... = correct
• Una capa de drenaje... = also possible, if it is indefinite
• Capa de drenaje... = usually sounds incomplete in a normal sentence

English often leaves articles out in labels or technical writing, but Spanish generally still wants one in a full sentence.

Because Spanish nouns have grammatical gender.

• capa is feminine → la capa
• agujero is masculine → el agujero

This is why the articles are different.

Also notice that the adjective or verb does not change here because there is no adjective agreeing with them in the sentence, and the verb agrees with the subject, not the object.

No. Another common word is orificio.

Both can work, but they can feel slightly different:

• agujero = more everyday, more general
• orificio = often more technical or formal

So depending on the context, you might also see:

• La capa de drenaje cubre el orificio de drenaje.

But agujero is perfectly natural.

Yes. Even though drenaje is a noun, the whole phrase de drenaje functions like a modifier.

It tells you what kind of layer and what kind of hole:

• capa → what kind? de drenaje
• agujero → what kind? de drenaje

So in practice, it behaves somewhat like an adjective in English, even though grammatically it is a prepositional phrase in Spanish.

A little, but the original order is the most natural and neutral:

• La capa de drenaje cubre el agujero de drenaje.

You could change the order for emphasis, but it may sound less neutral:

• El agujero de drenaje lo cubre la capa de drenaje.

That version emphasizes the drainage hole more.

For straightforward description, the original subject + verb + object order is best.

A rough pronunciation is:

• agujero ≈ ah-goo-HEH-ro

A few helpful points:

• the g in agu sounds like a normal hard g
• the j in -jero is a throaty Spanish sound, like a strong h
• the stress falls on je: aguJEro

And:

• capa ≈ KAH-pah
• drenaje ≈ dreh-NAH-heh
• cubre ≈ KOO-breh

Possibly, but cubre and tapa are not exactly the same.

• cubrir = to cover
• tapar = to cover up / block / plug

So:

• cubre focuses on the idea of being over the hole
• tapa often suggests blocking or sealing it

If the layer simply lies over the hole, cubre is a safe choice. If the idea is that it blocks or plugs the hole, tapa may fit better.

Yes. The present tense in Spanish is often used for:

• general truths
• habitual actions
• descriptions
• instructions in technical contexts

So La capa de drenaje cubre el agujero de drenaje can sound like a factual description of how something is arranged or designed.