Tiene el trasero sucio.

Tiene is the third-person singular of tener.

So, depending on context, it can mean:

• he has
• she has
• you have (formal singular, usted)

On its own, Tiene el trasero sucio does not tell you whether the person is male, female, or usted. You need context for that.

Because Spanish often drops subject pronouns when they are not needed.

The verb form tiene already tells you it is third-person singular, so Spanish usually leaves out él/ella/usted unless the speaker wants to add emphasis, contrast, or clarity.

So all of these are possible:

• Tiene el trasero sucio.
• Él tiene el trasero sucio.
• Ella tiene el trasero sucio.
• Usted tiene el trasero sucio.

The version without the pronoun is the most natural in many situations.

Spanish often uses the pattern:

tener + body part + adjective

So Tiene el trasero sucio literally works like He/She has the bottom dirty, which in natural English becomes His/Her bottom is dirty.

This structure is very common with body parts and physical conditions.

You can also say:

• Su trasero está sucio.

That is also correct, but it is built differently:

• tener + body part + adjective
• estar + adjective

Both can be natural, but the sentence you were given uses a very common Spanish pattern.

Because Spanish very often uses the definite article with body parts when the owner is already clear.

English usually says:

• his bottom
• her bottom
• your hand

Spanish often says:

• el trasero
• la mano
• la cabeza

if the context already makes it clear whose body part it is.

So:

• Tiene el trasero sucio = natural
• Tiene su trasero sucio = usually sounds unnecessary or unnatural in normal speech

Using su is more likely if you really want to emphasize ownership or avoid ambiguity.

In Spain, trasero is usually a fairly mild and everyday word. It is not especially formal, but it is also not as vulgar as culo.

Very roughly:

• trasero = mild, common, fairly safe
• culo = more vulgar/direct
• nalgas = more anatomical/formal, like buttocks

So if a learner wants a general, not-too-rude word for bottom/rear, trasero is a useful choice.

Because sucio agrees with trasero, and trasero is masculine singular.

Agreement in Spanish means the adjective changes to match the noun:

• el trasero sucio
• la mano sucia
• las nalgas sucias

So here:

• trasero = masculine singular
• therefore sucio = masculine singular

It describes el trasero, not the whole person.

So the sentence means that the person's bottom is dirty, not necessarily that the whole person is dirty.

Grammatically, the structure is:

• tiene = has
• el trasero = the bottom
• sucio = dirty

So sucio is linked to trasero.

Yes, but the given order is the most neutral and standard:

• Tiene el trasero sucio.

You may also hear:

• Tiene sucio el trasero.

That is possible, but it sounds more marked and may put more focus on sucio.

So for learners, the safest version to use is:

• Tiene el trasero sucio.

It normally means the whole bottom/rear as one body area.

Spanish often treats it as a single unit:

• el trasero = bottom / backside / rear

If you want to refer more specifically to the buttocks, you could use:

• las nalgas

But in normal everyday speech, el trasero refers to the whole area, not just one side.

Yes. Trasero can also mean rear, back part, or the part at the back of something.

For example, in other contexts it can refer to the back of an object, vehicle, or place.

But in Tiene el trasero sucio, it is understood as the body part because of the context and the phrase as a whole.

Yes. For Spain Spanish, it is a natural sentence.

It sounds like a normal way to say that someone's bottom is dirty, especially in contexts involving:

• children
• hygiene
• informal everyday speech
• joking or mildly embarrassed situations

It is not especially formal, but it is perfectly normal Spanish.