Si tu te sers de cette éponge, n’oublie pas de rincer l’évier ensuite.

Se servir de is a very common everyday way to say to use something. So Si tu te sers de cette éponge means If you use this sponge.

French could also use utiliser, and Si tu utilises cette éponge... would be correct too. But se servir de often sounds a little more natural in ordinary speech for physical objects.

The full verb is se servir de. It is a pronominal verb, so it normally comes with a reflexive pronoun:

• je me sers
• tu te sers
• il se sert

So the te is not optional here. It is part of the verb pattern. In this sentence, tu te sers de cette éponge simply means you use this sponge.

Because the expression is se servir de + noun.

So you say:

• se servir d’une éponge
• se servir d’un couteau
• se servir de cette éponge

That de belongs to the expression. English learners often want to translate word-for-word with just use, but in French this verb naturally takes de.

Because éponge is a feminine noun: une éponge.

The demonstrative adjectives are:

• ce for masculine singular
• cet for masculine singular before a vowel or mute h
• cette for feminine singular
• ces for plural

So:

• cet évier = this sink
• cette éponge = this sponge

Even though éponge starts with a vowel, it is still feminine, so cette is correct.

Because this is the imperative, used for commands and instructions.

In French, subject pronouns are usually dropped in the imperative:

• Oublie = forget
• N’oublie pas = don’t forget

So n’oublie pas de rincer l’évier means don’t forget to rinse the sink.

Compare that with the normal present tense:

• Tu n’oublies pas = you are not forgetting / you do not forget

That is a statement, not a command.

Because French uses oublier de + infinitive when you mean to forget to do something.

So:

• oublier de rincer = to forget to rinse
• oublier de fermer la porte = to forget to close the door

But if you forget a thing, French just uses the direct object:

• J’ai oublié mes clés = I forgot my keys

So in this sentence, n’oublie pas de rincer is the normal and correct pattern.

This is a very common French pattern:

• si + present tense, then
• imperative, present, or future in the main clause

Here it is:

• Si tu te sers de cette éponge = if you use this sponge
• n’oublie pas de rincer l’évier ensuite = don’t forget to rinse the sink afterwards

This is a real condition, not a hypothetical one. It means: if this situation happens, do this.

Ensuite means afterwards, then, or after that.

In this sentence, it tells you the order of actions:

1. use the sponge
2. rinse the sink afterwards

So ensuite helps show that the rinsing should happen after the sponge is used.

It is very natural at the end of the sentence here.

Because évier begins with a vowel sound. In French, le becomes l’ before a vowel or mute h.

So:

• le lavabo
• le mur
• l’évier

Also, évier is masculine: un évier.

So rincer l’évier means to rinse the sink.

Sers is pronounced roughly like ser in English-style spelling, with the final s silent.

So:

• tu te sers sounds roughly like tyu tə ser

A few other useful pronunciation notes in the sentence:

• éponge sounds roughly like ay-ponj
• évier sounds roughly like ay-vyay
• ensuite sounds roughly like ahn-sweet

As often happens in French, several final consonants are not pronounced, so the written form can look more complicated than the spoken one.