Purigu la ruston antaŭ ol meti grason.

In Esperanto, -u is the ending for the volitive form. In practice, this often works like an imperative or command.

So:

• purigi = to clean
• purigu = clean! / let someone clean

In this sentence, Purigu la ruston means Clean the rust or Remove the rust by cleaning.

For commands to you, Esperanto usually does not need a separate word for you:

• Purigu! = Clean!
• Purigu la ruston! = Clean the rust!

Because ruston is the direct object of purigu, it takes the accusative ending -n.

Compare:

• La rusto estas dika. = The rust is thick.
  Here rusto is the subject, so no -n.
• Purigu la ruston. = Clean the rust.
  Here ruston is the object, so it gets -n.

The la means the. It refers to the specific rust being talked about, probably the rust on the object in question.

So:

• rusto = rust
• la rusto = the rust
• la ruston = the rust, as a direct object

This is about how definite the noun is.

• la ruston = the specific rust that needs to be cleaned off
• grason = grease in a general sense, not a specific previously identified grease

In Esperanto, just like in English, you do not always use the with materials or substances when speaking generally.

So:

• meti grason = to apply grease / to put on grease
• meti la grason would suggest a particular grease already known from the context

In this sentence, the idea is probably before applying grease, not before applying the specific grease we already mentioned.

Antaŭ ol means before when it introduces an action.

• antaŭ = before
• ol = than, but it is also used in fixed expressions like antaŭ ol

In Esperanto, when you want to say before doing something or before someone does something, antaŭ ol is the normal pattern.

Examples:

• Antaŭ ol manĝi, lavu viajn manojn. = Before eating, wash your hands.
• Antaŭ ol iri, mi fermis la pordon. = Before leaving, I closed the door.

So in your sentence:

• antaŭ ol meti grason = before putting/applying grease

Because after antaŭ ol, Esperanto often uses the infinitive when the subject is general or understood from context.

• meti = to put / to place / to apply
• metu = put! / let someone put

So:

• antaŭ ol meti grason = before putting grease / before applying grease

If you said antaŭ ol metu grason, that would sound wrong here, because metu is a command form, not the form normally used after antaŭ ol in this kind of construction.

Yes. The subject is understood from context.

In Purigu la ruston antaŭ ol meti grason, the natural understanding is something like:

• Clean the rust before putting on grease
• in other words, before you put on grease or before one puts on grease

Esperanto often leaves the subject unstated when it is obvious or general.

If you wanted to make it explicit, you could say:

• Purigu la ruston antaŭ ol vi metas grason.

But the infinitive version is shorter and very natural.

Yes, you could, but it is a slightly different structure.

• antaŭ ol meti grason = before putting grease
• antaŭ ol vi metas grason = before you put grease

The infinitive version is often smoother and more general. The finite verb version explicitly names the subject.

Also, depending on style and context, some speakers might prefer a tense that fits the situation more clearly, for example:

• antaŭ ol vi metos grason = before you will put grease
• antaŭ ol vi metu grason is generally not the normal choice here

For a general instruction, antaŭ ol meti grason is very idiomatic.

Literally, meti means to put, to place, or to set. But in practical instructions, it often corresponds to English apply.

So:

• meti grason literally = put grease
• natural English meaning = apply grease

This is common in Esperanto: a simple verb like meti is often used where English chooses a more specialized verb.

For the same reason as ruston: it is the direct object of a verb.

Here the verb is meti:

• meti grason = to put/apply grease

Because graso is what is being put on, it becomes the object:

• graso → grason

So both objects in the sentence take -n:

• Purigu la ruston
• meti grason

Sometimes, yes, depending on context.

Purigi literally means to clean. In this sentence, cleaning the rust probably involves removing it, so English might naturally say:

• Clean off the rust
• Remove the rust

But the Esperanto verb itself is still purigi, not specifically forigi.

There is a slight difference:

• purigi = clean
• forigi = remove, get rid of

So Purigu la ruston focuses on cleaning it away, while Forigu la ruston would focus more directly on removing it.

Yes, Esperanto word order is fairly flexible, but the given order is the most natural and straightforward.

Standard order here is:

• Purigu la ruston antaŭ ol meti grason.

Because the accusative -n marks the objects, Esperanto can sometimes move words around without causing confusion. But in an instructional sentence like this, the ordinary order is best.

A learner should usually stick with the normal pattern:

• verb + object + time clause

That makes the sentence clear and natural.