Instalatorul deșurubează sifonul.

-ul is the definite article in Romanian here. It means the.

So:

• instalator = plumber
• instalatorul = the plumber
• sifon = siphon / trap
• sifonul = the siphon / the trap

Unlike English, Romanian usually puts the at the end of the noun instead of before it.

That is a normal feature of Romanian. The definite article is usually enclitic, meaning it gets attached to the end of the noun.

Compare:

• un instalator = a plumber

• instalatorul = the plumber

• un sifon = a siphon / a trap
• sifonul = the siphon / the trap

So Romanian often works like this:

• indefinite: separate word (un / o)
• definite: article attached to the noun

Deșurubează is the 3rd person singular present tense form of a deșuruba.

That means it can translate as:

• he/she unscrews
• he/she is unscrewing

In this sentence, the subject is instalatorul, so:

• Instalatorul deșurubează... = The plumber unscrews... / The plumber is unscrewing...

Romanian present tense often covers both the simple present and the present progressive idea in English.

Yes. They are closely related.

• șurub = screw (the noun)
• a șuruba = to screw in / fasten with a screw
• a deșuruba = to unscrew

The prefix de- often gives the idea of reversing an action, so a deșuruba is basically the opposite of a șuruba.

Mostly from word order and context.

In this sentence, Romanian uses the normal subject–verb–object order:

• Instalatorul = subject
• deșurubează = verb
• sifonul = object

So the sentence is understood as:

• The plumber unscrews the trap

In this particular sentence, both nouns have forms that look similar, so word order helps a lot. Romanian does not always mark the subject and object differently in a way that is visible on the noun itself.

Romanian often leaves out subject pronouns when they are not needed.

Because deșurubează already shows that the verb is 3rd person singular, Romanian does not need to say el unless there is special emphasis or contrast.

So Romanian normally says:

• Instalatorul deșurubează sifonul.

not:

• El instalatorul deșurubează sifonul. ❌

You could say El deșurubează sifonul if he is the subject and it is clear who he is, but here the noun instalatorul already gives the subject.

In this context, sifonul most likely means the sink trap or drain trap under a sink.

The word sifon can have different meanings depending on context, such as:

• siphon
• trap in plumbing
• sometimes even soda siphon in other contexts

Because the subject is a plumber, the plumbing meaning is the natural one here.

Because sifonul is an inanimate direct object.

Romanian often uses pe before a direct object when it is:

• a person
• an animate being
• or a strongly specific/pronominal object

For example:

• Văd omul.
• Îl văd pe om.

But with an inanimate object like sifonul, Romanian normally just says:

• deșurubează sifonul

without pe.

Because instalator is masculine, and sifon is neuter, and in Romanian neuter nouns behave like masculine nouns in the singular.

So:

• instalator → instalatorul
• sifon → sifonul

That is why both take -ul here.

A useful detail:

• masculine singular definite often uses -ul
• neuter singular definite also often uses -ul

But in the plural, neuter nouns behave like feminine nouns.

A rough English-friendly pronunciation is:

deh-shu-roo-BE-a-zuh

A few important sound notes:

• ș = sh as in ship
• ă = a short central vowel, something like the a in about
• ea in -bează is pronounced together, not as two completely separate syllables

So deșurubează sounds approximately like:

deh-shu-roo-BE-a-zuh

A simple approximation is:

in-sta-la-TO-rul deh-shu-roo-BE-a-zuh see-FO-nul

Stress usually falls like this:

• instalaTOrul
• deșuruBEAză
• siFOnul

This is only an approximation, but it is good enough to help you start saying the sentence naturally.