Tanto el rímel resistente al agua como el pintalabios salen mejor con un buen desmaquillante.

It means both ... and ....

So:

• Tanto el rímel resistente al agua como el pintalabios... = Both waterproof mascara and lipstick...

This structure is very common in Spanish when you want to link two things with equal importance.

A few more examples:

• Tanto Juan como Ana vienen.
  = Both Juan and Ana are coming.
• Me gustan tanto el café como el té.
  = I like both coffee and tea.

It is not usually translated word-for-word as as much... as here. In this sentence, the natural English meaning is simply both ... and ....

Because the subject is plural: it refers to two things together:

• el rímel resistente al agua
• el pintalabios

When Spanish uses tanto X como Y, the verb normally agrees with both items together, so it becomes plural:

• Tanto X como Y salen...

That is why it is:

• salen mejor
  not
• sale mejor

Compare:

• El rímel sale mejor... = Mascara comes off better...
• El pintalabios sale mejor... = Lipstick comes off better...
• Tanto el rímel como el pintalabios salen mejor... = Both mascara and lipstick come off better...

Yes, salir often means to go out / leave / come out, but in contexts like makeup, stains, dirt, or marks, it can also mean to come off or to be removed.

So here:

• salen mejor means
• come off better / are removed more easily

This is a very natural use in Spanish.

Examples:

• Esta mancha no sale.
  = This stain won’t come out.
• El maquillaje sale con agua micelar.
  = The makeup comes off with micellar water.

English learners often expect quitar here, and that can also work in some structures, but salir is very idiomatic when talking about whether something comes off easily.

Yes, se quitan mejor would also be understandable and natural in many contexts.

Compare:

• salen mejor = come off better / come off more easily
• se quitan mejor = can be removed better / are easier to remove

The difference is mostly one of perspective:

• salir focuses on the makeup itself coming off
• quitar focuses more on removing it

So:

• El pintalabios sale mejor con aceite.
• El pintalabios se quita mejor con aceite.

Both are fine. In product descriptions or advice, salir mejor sounds very natural.

In this context, yes: resistente al agua is the usual equivalent of waterproof or water-resistant for cosmetics.

Literally, it means:

• resistente = resistant
• al agua = to water

So rímel resistente al agua means waterproof mascara.

A small nuance:

• resistente al agua literally sounds closer to water-resistant
• but in makeup language, it is commonly used where English would often say waterproof

You may also see waterproof itself in advertising, but resistente al agua is the more Spanish way to say it.

Because a + el contracts to al in Spanish.

So:

• a + el agua → al agua

This contraction is normally mandatory.

Examples:

• Voy al supermercado.
  = I’m going to the supermarket.
• Es resistente al calor.
  = It is heat-resistant.
• Es resistente al agua.
  = It is water-resistant / waterproof.

One important exception is when el is part of a proper name:

• Voy a El Escorial.
  not al Escorial

But here agua is just a normal noun, so al agua is correct.

Desmaquillante means makeup remover.

It comes from the verb desmaquillar, meaning to remove makeup from someone / to take someone’s makeup off.

So:

• un desmaquillante = a makeup remover
• desmaquillarse = to remove one’s makeup

Examples:

• Necesito un desmaquillante suave.
  = I need a gentle makeup remover.
• Siempre me desmaquillo antes de dormir.
  = I always remove my makeup before sleeping.

In Spain, desmaquillante is a very common word in skincare and cosmetics.

Because bueno becomes buen before a singular masculine noun.

So:

• un buen desmaquillante not
• un bueno desmaquillante

This is a normal shortening of bueno before masculine singular nouns.

Compare:

• un buen libro = a good book
• un buen día = a good day
• un buen desmaquillante = a good makeup remover

But if the adjective comes after the noun, it stays bueno:

• un desmaquillante bueno

That said, un buen desmaquillante sounds more natural here.

Because that is simply their grammatical gender in Spanish:

• el rímel
• el pintalabios

Grammatical gender does not always match any logical real-world category. You just need to learn the noun together with its article.

A few notes:

• rímel is masculine in standard usage: el rímel
• pintalabios is also masculine: el pintalabios

This is a good reminder that in Spanish, you should memorise nouns as:

• el rímel, not just rímel
• el pintalabios, not just pintalabios

In Spain, rímel is very common and widely understood.

You may also hear:

• máscara de pestañas

Both mean mascara, but the feel is a bit different:

• rímel = very common everyday word
• máscara de pestañas = more descriptive, sometimes a bit more formal or product-like

In Spain, rímel is especially common in everyday speech.

So a Spanish learner should recognise both:

• Me he comprado un rímel nuevo.
• Me he comprado una máscara de pestañas nueva.

Both mean I bought a new mascara.

The accent mark shows the stress:

• rí-mel

Without getting too technical, Spanish spelling rules would not normally place the stress there unless it is marked, so the written accent tells you the word is stressed on the first syllable.

Pronunciation is roughly:

• REE-mel

This is useful because many English speakers are tempted to say it more like English rimel or rimmel, but in Spanish the stress is clearly on rí.

Mejor means better.

In this sentence, it means that these products come off better / more effectively / more easily when you use a good makeup remover.

So:

• salen mejor con un buen desmaquillante

suggests something like:

• come off better with a good makeup remover
• are removed more effectively with a good makeup remover

It does not necessarily mean perfectly or completely by itself; it just says the result is better than with other methods.

Yes. Here con means with / by using.

So:

• salen mejor con un buen desmaquillante = they come off better with a good makeup remover = they come off better when you use a good makeup remover

This is a very common use of con to express means or instrument.

Examples:

• Se corta con un cuchillo.
  = It is cut with a knife.
• Se limpia mejor con agua caliente.
  = It cleans better with hot water.

Yes, some changes are possible, but the original order is very natural.

Original:

• Tanto el rímel resistente al agua como el pintalabios salen mejor con un buen desmaquillante.

Possible variation:

• El rímel resistente al agua y el pintalabios salen mejor con un buen desmaquillante.

This is simpler and also correct.

However, tanto ... como ... gives a slightly more balanced, polished feel. It is especially common in written advice, advertising, and explanatory text.

So if you are aiming for natural, slightly more polished Spanish, the original structure works very well.