Learn Hardcore French: Je rince la fourchette dans l'évier, car elle est couverte de beurre salé. - I rinse the fork in the sink, because it is covered with salted butter.

rincer = to rinse, usually with water only, to remove residue (soap, salt, crumbs). Example: Je rince la fourchette.
laver = to wash thoroughly, typically with water and soap/detergent. Example: Je lave les assiettes.
nettoyer = to clean (more general), i.e., make something clean; can involve wiping, scrubbing, products. Example: Je nettoie l’évier.

Why is it couverte and not couvert?

Because it agrees in gender and number with the noun it describes. Couverte (past participle used as an adjective) matches the feminine singular la fourchette. If it were masculine singular (e.g., le couteau), you’d say couvert; plural feminine would be couvertes.

Why is it couverte de beurre salé and not couverte du beurre salé or couverte avec du beurre salé?

The idiomatic pattern is adjective + de
- substance: couvert(e) de, plein(e) de, garni(e) de, orné(e) de.
avec is possible but less idiomatic here.
du can appear if you mean “covered with the (specific) salted butter” already identified in context, but for the general idea “covered with salted butter,” use de: couverte de beurre salé.

Can I replace car with parce que or puisque? Any nuance?

car = “for/because” giving an explanation; a bit more written or neutral and not used to directly answer “Pourquoi ?”.
parce que = everyday “because”; used in speech and to answer “Pourquoi ?”.
puisque = “since/as,” when the cause is assumed to be known/obvious. All three work here; the choice is about tone and context.

Is the comma before car necessary?

It’s standard to place a comma before car in French: …, car …. Your sentence’s comma is correct and stylistically expected.

Why dans l’évier and not à l’évier? And is évier the kitchen sink?

dans l’évier = literally in the sink basin (appropriate for rinsing).
à l’évier (“at the sink”) is uncommon/nonnative in this context.
You can also say sous le robinet (under the tap).
évier is the kitchen sink; the bathroom sink is the lavabo.

Why use the definite article la fourchette instead of une fourchette or a possessive?

French typically needs an article. Use:

la fourchette if it’s context-specific/identifiable.
une fourchette if it’s any/one fork, newly introduced.
ma/ta/sa fourchette if you want to specify ownership.

Who does elle refer to—why not il?

Elle refers to la fourchette (feminine). L’évier and le beurre are masculine, so they’d take il. Agreement of pronouns follows the grammatical gender of the noun, not the object’s “real-world” gender.

Why is it beurre salé and not beurre salée?

The adjective salé agrees with beurre (masculine singular), not with fourchette. Hence beurre salé. Adjectives generally agree with the noun they modify.

What’s going on with the apostrophe in l’évier?

It’s elision: le évier becomes l’évier because évier begins with a vowel sound. The accent on é is required: évier, not “evier”.

Why is it spelled je rince and not something with a cedilla, like je rinçe?

Before e, the letter c is already pronounced /s/, so no cedilla is needed. You only add a cedilla to keep the /s/ sound before a, o, u: nous rinçons. Present-tense forms:

je rince, tu rinces, il/elle rince, nous rinçons, vous rincez, ils/elles rincent.

Can I replace de beurre salé with the pronoun en?

Yes, if the referent is clear. Example: Je rince la fourchette, car elle en est couverte. Here en replaces de beurre salé and comes before the verb est.

Difference between couvert(e) and recouvert(e)?

Both can mean “covered,” but recouvert(e) can imply “covered again” or “covered all over/entirely.” In many contexts, they’re close in meaning; couvert(e) is perfectly fine here.

Could/should I use a past tense if the action is finished?

Yes. For a completed action, use the passé composé: J’ai rincé la fourchette dans l’évier, car elle était couverte de beurre salé. The cause/background (était couverte) is naturally in the imperfect.

Why is the adjective salé placed after beurre?

Most adjectives in French, including flavors and physical qualities, follow the noun: beurre salé, pain frais, viande crue. Only certain adjective types typically come before (e.g., small set like beau, grand, petit).

Are there other natural ways to express the place/instrument of rinsing?

Yes:

Place: Je rince la fourchette sous le robinet.
Instrument: Je rince la fourchette à l’eau froide. All are idiomatic; choose the one that matches what you want to emphasize (location vs. water).