Por mucho que limpie el felpudo, el sótano sigue oliendo mal cuando llueve.

It means no matter how much or however much. It introduces a concessive idea: the action in that clause does not change the result in the main clause.

So Por mucho que limpie el felpudo... means that cleaning the doormat does not solve the problem. A very similar expression is por más que.

Because por mucho que normally takes the subjunctive.

Here, limpie is the present subjunctive of limpiar. Spanish uses the subjunctive after this expression because the effort in that clause is presented as something that does not affect the outcome.

So:

• Por mucho que limpie... = correct
• Por mucho que limpia... = not correct in this structure

Spanish often leaves out subject pronouns when they are understood from context.

The form limpie can mean:

• I clean
• he/she cleans
• you clean in the formal singular usted

So the sentence itself does not tell you exactly who is cleaning. You need context, or the translation already provided to the learner.

No. Even though limpie can also be a formal command form in other contexts, here it is not an imperative.

In this sentence, it is a subjunctive verb because it comes after por mucho que:

• Por mucho que limpie el felpudo...

So it means no matter how much ... cleans, not clean the doormat.

In Spain, felpudo usually means doormat, especially the mat by the entrance of a home.

It is a very common Peninsular Spanish word. In some contexts, English speakers may think of mat more generally, but felpudo specifically suggests the entrance mat you wipe your shoes on.

Because Spanish often uses seguir + gerund to mean to keep doing something, to continue doing something, or to still be doing something.

So:

• sigue oliendo mal = still smells bad / keeps smelling bad

The subject of sigue is el sótano.

Because oler has an irregular gerund: oliendo.

This is just one of the irregular forms of oler, which is an irregular verb in several parts of its conjugation. For example:

• huelo
• hueles
• huela
• oliendo

So sigue oliendo is the normal, correct form.

Because after verbs like oler, Spanish normally uses mal, not malo.

So:

• huele mal = it smells bad
• sabe mal = it tastes bad

Even though English uses bad here, Spanish uses mal in this pattern. Malo is an adjective, so it goes with nouns:

• un mal olor
• un olor malo although un mal olor is more natural

In this sentence, oliendo mal is exactly what you would expect.

Because this sentence describes a habitual or general situation: whenever it rains, the basement smells bad.

With habitual facts, Spanish uses the indicative:

• cuando llueve = when it rains / whenever it rains

If the sentence were referring to a future event, Spanish would usually use the subjunctive:

• cuando llueva, veremos qué pasa

Huele mal simply says it smells bad.

Sigue oliendo mal adds the idea that this was already true before and it is still true now. So sigue gives a sense of continuation:

• huele mal = smells bad
• sigue oliendo mal = still smells bad / continues to smell bad

Because Spanish normally uses the definite article with specific nouns that are identifiable in the context.

Here, the speaker is talking about a particular doormat and a particular basement, so el is natural:

• el felpudo
• el sótano

In English, you might sometimes use the, or sometimes a possessive like my, depending on context. Spanish often prefers the article when the reference is already clear.

Because sótano is stressed on the third-to-last syllable: SÓ-ta-no.

In Spanish, words stressed on the third-to-last syllable, called esdrújulas, always take a written accent. So the accent in sótano is required.