Il faut que nous nettoyions la litière tous les jours ; sinon le chaton miaule devant la porte.

Il faut que is a very common French structure meaning it is necessary that... or we have to... when a full clause follows.

• Il faut + infinitive: used when you do not name the subject of the action
  
  • Il faut nettoyer la litière. = It is necessary to clean the litter box.
• Il faut que + subject + subjunctive: used when you do name the subject
  
  • Il faut que nous nettoyions la litière. = We have to clean the litter box.

So here, because the sentence explicitly says nous, French uses il faut que + a verb in the subjunctive.

Because il faut que normally requires the subjunctive mood.

French uses the subjunctive after expressions of:

• necessity
• obligation
• emotion
• doubt
• possibility
• judgment

Since il faut que expresses necessity, the next verb must usually be in the subjunctive:

• que nous nettoyions

This is not optional in standard French.

Nettoyions is the 1st person plural present subjunctive of nettoyer.

The present subjunctive endings are based on the ils form of the present tense, with subjunctive endings added.

For nettoyer:

Present indicative:

• je nettoie
• tu nettoies
• il nettoie
• nous nettoyons
• vous nettoyez
• ils nettoient

Present subjunctive:

• que je nettoie
• que tu nettoies
• qu’il nettoie
• que nous nettoyions
• que vous nettoyiez
• qu’ils nettoient

The -yions spelling can look strange, but it is correct.

This is a very common learner question because nettoyions looks unusual.

The form comes from:

• the verb stem with y
• plus the subjunctive ending for nous, which is -ions

So:

• nettoy- + ions = nettoyions

That is why you get yi next to each other. It is not a typo.

The same thing happens with similar verbs:

• que nous envoyions
• que nous appuyions
• que nous essuyions

It is pronounced approximately like neh-twa-YON.

A rough breakdown:

• netto- sounds like neh-twa
• yions sounds like yon

The important thing is that it does not sound like every written vowel separately. The spelling is more complex than the pronunciation.

Also note that:

• nous nettoyons and que nous nettoyions are pronounced very similarly, though not always exactly the same depending on speaker and style.

La litière usually means litter or litter box/litter tray, depending on context.

With a cat, nettoyer la litière most often means:

• to clean the cat litter
• or more naturally in English, to clean the litter box

French often uses la litière where English may prefer the litter box.

Tous les jours means every day or each day.

It is a fixed, very common expression:

• Je marche tous les jours. = I walk every day.
• On nettoie la litière tous les jours. = We clean the litter box every day.

Be careful not to confuse:

• tous les jours = every day
• tout le jour = all day long

Those are different meanings.

Here sinon means otherwise.

It introduces the consequence if the first action is not done:

• Il faut que nous nettoyions la litière tous les jours ; sinon...
• We have to clean the litter box every day; otherwise...

It can also mean if not, depending on context, but otherwise is the most natural understanding here.

Le chaton means kitten, while le chat means cat.

So the sentence specifically refers to a young cat. French uses the diminutive noun chaton rather than adding an adjective like small cat.

Miaule comes from the verb miauler, which means to meow.

Here:

• le chaton miaule = the kitten meows

This is the:

• 3rd person singular present tense

Conjugation:

• je miaule
• tu miaules
• il/elle miaule
• nous miaulons
• vous miaulez
• ils/elles miaulent

Devant la porte means in front of the door.

• devant = in front of / before
• la porte = the door

It is used because the kitten is positioned outside or near the door, meowing there.

Compare:

• devant la porte = in front of the door
• à la porte = at the door
• derrière la porte = behind the door

French often chooses the preposition based on the exact spatial idea the speaker wants.

The semicolon separates two closely related ideas:

1. the obligation
2. the consequence if you do not do it

So:

• Il faut que nous nettoyions la litière tous les jours ; sinon le chaton miaule devant la porte.

A comma is also sometimes seen in informal writing, but the semicolon is a neat way to join two complete, closely connected clauses. It is a punctuation choice showing a stronger break than a comma, but less final than a period.

Yes. French has several ways to express obligation.

For example:

• Nous devons nettoyer la litière tous les jours.
• Il faut nettoyer la litière tous les jours.
• Il faut que nous nettoyions la litière tous les jours.

They are all correct, but they are structured differently:

• nous devons + infinitive = we must / we have to
• il faut + infinitive = it is necessary to...
• il faut que + subjunctive = it is necessary that we...

The original sentence is slightly more formal or structured, and it is very useful because it shows a common trigger for the subjunctive.

Both are possible, but they feel a little different.

• nous is more formal, careful, or written
• on is more common in everyday spoken French for we

So in casual speech, many people might say:

• Il faut qu’on nettoie la litière tous les jours...

That is extremely natural in conversation.

The original sentence with nous nettoyions is absolutely correct, but it sounds a bit more formal or textbook-like than qu’on nettoie.