Learn Hardcore Greek: Στο σπίτι η κουζίνα σφουγγαριζόταν κάθε βράδυ όταν ήμουν παιδί. - At home the kitchen was mopped every evening when I was a child.

In this sentence, the imperfect shows a repeated, habitual action in the past:
η κουζίνα σφουγγαριζόταν κάθε βράδυ = the kitchen used to be mopped every night.

Why do we use the imperfect (σφουγγαριζόταν) instead of an aorist form?

In Greek, the imperfect describes:

Ongoing past actions
Repeated / habitual past actions
Background situations

Here we have κάθε βράδυ (every evening) and όταν ήμουν παιδί (when I was a child). Both clearly describe something that happened regularly over a period of time in the past.

Using the imperfect σφουγγαριζόταν matches that idea:
It used to be mopped / It was mopped every night (as a routine).

An aorist passive like σφουγγαρίστηκε would sound more like a single completed event:

Η κουζίνα σφουγγαρίστηκε χτες. – The kitchen was mopped yesterday. (once)

Why is the sentence in the passive: η κουζίνα σφουγγαριζόταν, instead of an active form like “we mopped the kitchen”?

Greek, like English, often uses the passive when:

The doer is not important, not specified, or obvious from context.
The result or the affected thing (here: the kitchen) is the focus.

Η κουζίνα σφουγγαριζόταν κάθε βράδυ focuses on the state of the kitchen and the regular cleaning routine.

You could say it actively:

Στο σπίτι σφουγγαρίζαμε την κουζίνα κάθε βράδυ όταν ήμουν παιδί.
At home, we used to mop the kitchen every night when I was a child.

This makes σφουγγαρίζαμε (we used to mop) the focus and explicitly introduces we as the subject.
The original passive version leaves the subject vague (maybe the parents, maybe “we”), and emphasizes the routine applied to the kitchen itself.

What is the subject of σφουγγαριζόταν in this sentence?

The subject is η κουζίνα (the kitchen).

Even though η κουζίνα is not doing the action, in the passive voice the subject is the thing that undergoes the action. So grammatically:

Subject: η κουζίνα
Verb: σφουγγαριζόταν
Agent (unexpressed): by someone (parents, family, etc.)

In Greek passive sentences, it is normal that the subject is the receiver of the action.

Why is it η κουζίνα with a definite article? Could we just say κουζίνα?

In Greek, definite articles are used much more often than in English. We say:

η κουζίνα = the kitchen (specific, known from context)
μια κουζίνα = a kitchen (some kitchen, not specific)
κουζίνα (without article) is rare as a full subject in standard usage; it sounds incomplete or very generic.

Here we clearly mean the specific kitchen of the house, so Greek naturally uses the article:

Στο σπίτι η κουζίνα σφουγγαριζόταν… – At home, the kitchen was mopped…

The possessor (our kitchen, our house’s kitchen) is understood from context; Greek usually does not need a possessive like our here, because στο σπίτι and the context already make that clear.

What is the role of στο σπίτι at the beginning, and how is it different from just σπίτι or στο σπίτι μας?

στο σπίτι = σε + το σπίτι = at the house / at home.

Στο σπίτι η κουζίνα σφουγγαριζόταν…
Literally: At the house, the kitchen was mopped…
Function: sets the location / context: we are talking about what happened at home.

Compare:

Σπίτι η κουζίνα σφουγγαριζόταν… – without στο this sounds wrong; you need the preposition (σε) and the article (το) here.
Στο σπίτι μας η κουζίνα σφουγγαριζόταν… – In our house, the kitchen was mopped…
Adds explicit our, making the possessive clear.

In everyday speech, στο σπίτι almost always implies “at home (our home)” unless the context says otherwise.

Can the word order be different, for example Η κουζίνα στο σπίτι σφουγγαριζόταν κάθε βράδυ? Does the meaning change?

Yes, Greek word order is fairly flexible, and these are all grammatical:

Στο σπίτι η κουζίνα σφουγγαριζόταν κάθε βράδυ όταν ήμουν παιδί.
Η κουζίνα στο σπίτι σφουγγαριζόταν κάθε βράδυ όταν ήμουν παιδί.
Η κουζίνα σφουγγαριζόταν στο σπίτι κάθε βράδυ όταν ήμουν παιδί.

The basic meaning stays the same. The changes affect emphasis and flow:

Starting with Στο σπίτι emphasizes the context/place: At home, (what happened was that) the kitchen was mopped…
Starting with Η κουζίνα puts more immediate focus on the kitchen as the topic.

All of them are natural; the original just foregrounds the home setting.

What does κάθε βράδυ do grammatically, and can it be moved to other positions?

κάθε βράδυ means every evening / every night and functions as a time adverbial.

In Greek, adverbials of time are fairly free in position. All of these are possible:

Στο σπίτι η κουζίνα σφουγγαριζόταν κάθε βράδυ όταν ήμουν παιδί.
Κάθε βράδυ, στο σπίτι η κουζίνα σφουγγαριζόταν όταν ήμουν παιδί.
Στο σπίτι η κουζίνα κάθε βράδυ σφουγγαριζόταν όταν ήμουν παιδί.
Στο σπίτι η κουζίνα σφουγγαριζόταν όταν ήμουν παιδί, κάθε βράδυ. (more marked)

The most neutral is usually before or after the verb, as in the original.
Its presence also strongly invites the imperfect tense, since it suggests a regular habit.

How does όταν ήμουν παιδί work grammatically, and why is ήμουν (imperfect) used?

όταν ήμουν παιδί is a time clause:

όταν = when
ήμουν = I was (imperfect of είμαι)
παιδί = child

So it means when I was a child / when I was little.

We use ήμουν (imperfect) because it describes a state over a period of time in the past (your childhood), not a single event. Greek usually uses the imperfect in όταν-clauses when talking about:

habitual actions in the past
ongoing or extended states in the past

Compare:

Όταν ήμουν παιδί, η κουζίνα σφουγγαριζόταν κάθε βράδυ.
When I was a child, the kitchen used to be mopped every night.

Note: You may also see the colloquial form ήμουνα instead of ήμουν; both are correct, ήμουν is slightly more neutral/standard.

Should there be a comma before όταν ήμουν παιδί?

You will often see both versions:

Στο σπίτι η κουζίνα σφουγγαριζόταν κάθε βράδυ όταν ήμουν παιδί.
Στο σπίτι η κουζίνα σφουγγαριζόταν κάθε βράδυ, όταν ήμουν παιδί.

In modern Greek punctuation, a comma is usually added if the όταν-clause is felt as a separate, additional piece of information (like an aside or clear time frame), especially when it comes after the main clause.

Here, many writers would naturally put a comma:

…κάθε βράδυ, όταν ήμουν παιδί.

Without the comma, it is still correct; it just reads a bit more tightly as one continuous flow. So this is more a matter of style and rhythm than strict grammar.

How is σφουγγαριζόταν pronounced and why are there two gammas (γγ) in σφουγγαρίζω?

σφουγγαριζόταν is pronounced approximately:

[sfuŋɡariˈzothan]
- σφου- like sfoo
- γγ = [ŋɡ], like the ng in finger (not exactly like singer)
- stress on -ζό-: σφουγγαριζόταν

In Modern Greek spelling:

γγ, γκ, γχ, γξ represent combinations with a nasal + voiced stop
So σφουγγαρίζω reflects the noun σφουγγάρι (sponge), with that γγ cluster.

The stress pattern is:

Present passive: σφουγγαρίζεται (stress on -ρί-)
Imperfect passive 3rd sg.: σφουγγαριζόταν (stress moves to -ζό-)

Is σφουγγαριζότανε also correct? What is the difference from σφουγγαριζόταν?

Yes, σφουγγαριζότανε is a colloquial / alternative form of σφουγγαριζόταν.

σφουγγαριζόταν – more standard, typical of written Greek
σφουγγαριζότανε – very common in spoken Greek, especially in many dialects and informal styles

Meaning and grammar are identical: both are 3rd person singular, imperfect passive.

In writing (especially in more formal contexts), σφουγγαριζόταν is preferred. In everyday speech you will hear both.

If I wanted to make it plural, for example “the kitchens were mopped every night”, how would the verb change?

Then your subject becomes plural, so the verb must also be 3rd person plural in the imperfect passive:

Οι κουζίνες σφουγγαρίζονταν κάθε βράδυ όταν ήμουν παιδί.
- Οι κουζίνες – the kitchens (plural)
- σφουγγαρίζονταν – they were being mopped / used to be mopped

So:

Singular: η κουζίνα σφουγγαριζόταν
Plural: οι κουζίνες σφουγγαρίζονταν

Same tense and voice, different number agreement.