Vaciamos el contenedor de posos, ya que está lleno.

Yes, vaciamos is the 1st person plural present of vaciar: we empty.

But in Spanish, especially in instructions, recipes, manuals, and guided steps, this form is often used to mean something like:

• we empty the container
• let’s empty the container
• or even an impersonal instruction like empty the container

So depending on context, it may sound more natural in English as an instruction rather than a statement about what we usually do.

Because Spanish often drops subject pronouns when the verb already makes the subject clear.

• vaciamos already tells you the subject is we
• so nosotros vaciamos is usually unnecessary

Spanish only adds nosotros if the speaker wants emphasis, contrast, or clarity.

For example:

• Vaciamos el contenedor = We empty the container
• Nosotros vaciamos el contenedor = We empty the container (maybe not someone else)

Posos usually means grounds, dregs, or sediment, depending on context.

In a sentence about a contenedor de posos, the most likely meaning is:

• coffee grounds
• or more generally residue left behind

In Spain, this phrase is very common with coffee machines, where el contenedor de posos is the container that collects used coffee grounds.

Both are possible in some contexts, but they are not exactly the same.

• contenedor de posos = grounds container / container of-for grounds
  This is the normal, natural label for the type of container.
• contenedor para posos = container for grounds
  This is understandable, but sounds a bit more explanatory and less like the standard name.

Spanish often uses de to name or classify things:

• taza de café = coffee cup
• máquina de lavar = washing machine
• contenedor de posos = grounds container

So de posos tells you what kind of container it is.

Because it refers to a specific, known container.

The sentence is not talking about any random container. It means the particular one relevant in the situation, probably the coffee machine’s grounds container.

Spanish uses the definite article el/la/los/las very often when the object is already understood from context.

So:

• el contenedor = the container
• un contenedor = a container

Here, el is the natural choice.

Both can mean because, but ya que often sounds a bit more like:

• since
• as
• given that

It often introduces a reason that is presented as obvious, known, or explanatory.

So:

• Vaciamos el contenedor porque está lleno = We empty the container because it is full
• Vaciamos el contenedor, ya que está lleno = We empty the container, since it is full

In this sentence, ya que sounds a little more explanatory and slightly more formal. It is very natural in written instructions or neutral narration.

Because full is treated as a state or condition, so Spanish uses estar, not ser.

• estar lleno = to be full
• ser is used for identity, inherent characteristics, origin, etc.

So:

• El contenedor está lleno = The container is full

This is one of the classic ser vs estar differences: temporary or resulting conditions usually take estar.

Está refers back to el contenedor.

Spanish often avoids repeating the noun when the reference is already clear:

• Vaciamos el contenedor de posos, ya que está lleno = We empty the grounds container, since it is full

English needs it, but Spanish can simply use the verb and adjective without repeating the subject.

You also know the hidden subject is el contenedor because lleno is:

• masculine singular

That matches contenedor.

Because lleno agrees with contenedor, which is a masculine singular noun.

In Spanish, adjectives usually agree in gender and number with the noun they describe.

• el contenedor → masculine singular
• so: lleno

Compare:

• el contenedor está lleno
• la bandeja está llena
• los contenedores están llenos
• las bandejas están llenas

Because in Spanish, posos is commonly used in the plural to refer to grounds, dregs, or sediment as a substance made up of many small remains.

This is similar to how English often uses plural-style words like grounds.

There is also a singular poso, but it more often refers to:

• a deposit
• sediment at the bottom
• a residue left behind

In the context of coffee machines, posos is the normal form.

Because the second part gives an explanatory reason for the first part.

• Vaciamos el contenedor de posos, ya que está lleno.

That comma helps separate:

1. the main action: Vaciamos el contenedor de posos
2. the explanation: ya que está lleno

With ya que, this punctuation is very common, especially in written Spanish. It makes the sentence clearer and more natural.