No metemos detergente en polvo en compartimentos de suavizante.

Metemos is the 1st person plural present indicative of meter.

• meter = to put in / insert
• metemos = we put / we are putting

So grammatically, the sentence is built like a normal present-tense statement, not like a standard imperative.

Spanish sometimes uses the present tense to express a rule, routine, or general instruction, especially in notices, manuals, or institutional language.

So No metemos... literally looks like we do not put..., but in context it can mean something like:

• we don’t put X here
• X is not put here
• do not put X here

It can sound a bit more collective or impersonal than a direct command.

That said, a more standard warning aimed directly at the reader would often be:

• No ponga detergente en polvo...
• No eche detergente en polvo...
• No meter detergente en polvo... on a sign

All three can be possible, but meter is very common in Spain when talking about putting something into a machine, compartment, drawer, bag, box, etc.

Here the idea is very physical: putting something into a compartment. That makes meter a natural choice.

Roughly:

• meter = put in / insert
• poner = put / place
• echar = pour in / throw in / add

In washing-machine instructions, you might hear any of them, but meter sounds very natural for inserting something into a compartment.

Because Spanish often omits the article when talking about a substance or category in a general sense.

Here detergente en polvo means powder detergent as a type of product, not a specific detergent already identified.

Compare:

• No metemos detergente en polvo... = we do not put powder detergent...
• No metemos el detergente en polvo... = we do not put the powder detergent...
  now it sounds like a specific detergent already known in the conversation

This is very common with mass nouns and product names used generically.

En polvo means in powder form or simply powdered.

So:

• detergente en polvo = powder detergent

This is a fixed and very common Spanish pattern:

• leche en polvo = powdered milk
• chocolate en polvo = powdered chocolate
• ajo en polvo = garlic powder

So the first en is part of the expression en polvo, not the preposition introducing the compartment.

Because they are doing two different jobs:

1. detergente en polvo
   Here en belongs to the expression en polvo, meaning powdered / in powder form.

2. en compartimentos de suavizante
   Here en means in / into the softener compartments.

So although the same word appears twice, the structure is different each time.

With verbs of putting or placing, Spanish often uses en where English uses in or into.

So:

• meter algo en un compartimento
• literally: put something in a compartment
• naturally in English: put something into a compartment

Spanish does not need a separate word exactly like English into in many cases. En is often enough.

Because de + noun without article often describes the type, function, or purpose of something.

So:

• compartimentos de suavizante = softener compartments / compartments for softener

This is similar to:

• botella de agua = water bottle
• taza de café = coffee cup
• máquina de lavar = washing machine

If you said del suavizante, it would sound more like of the specific softener already mentioned, not softener compartments as a category.

The plural makes the statement more general: it applies to softener compartments in general, not just one specific compartment.

And the lack of article also helps keep it generic.

So:

• en compartimentos de suavizante = in softener compartments, generally
• en los compartimentos de suavizante = in the softener compartments, a more specific set
• en el compartimento de suavizante = in the softener compartment, one specific compartment

On instructions and labels, Spanish often prefers this more general article-free style.

Yes. In the context of laundry and washing machines, suavizante means fabric softener.

By itself, suavizante can literally mean softener, but in this context Spanish speakers automatically understand it as the laundry product.

So compartimentos de suavizante means the section of the detergent drawer meant for fabric softener.

It is understandable and grammatical, but many speakers in Spain would probably expect a slightly more standard instruction such as:

• No ponga detergente en polvo en el compartimento del suavizante.
• No eche detergente en polvo en el compartimento del suavizante.
• No meter detergente en polvo en el compartimento del suavizante.
  common on signs and labels

So the original sentence works, but it has a somewhat institutional or unusual feel compared with the most typical wording on a washing-machine label.