Learn Hardcore Finnish: Tyhjennän astianpesukoneen myöhemmin ja laitan astiat hyllylle. - I will empty the dishwasher later and put the dishes on the shelf.

It marks first person singular present: I empty, I put. Finnish normally uses the present to talk about the future when a time word like myöhemmin (later) is present, so it corresponds to English I’ll empty / I’ll put here.

Why is it tyhjennän even though the dictionary form is tyhjentää?

In many type-1 verbs ending in -ntaa/-ntää, the cluster nt becomes nn in most present-tense personal forms:

tyhjentää → tyhjennän, tyhjennät, tyhjennämme, tyhjennätte; but 3rd persons keep nt: tyhjentää, tyhjentävät
Compare: antaa → annan, lentää → lennän

Why is it astianpesukoneen (with -n) and not just astianpesukone?

Because it’s a total (complete) object. Finnish marks a complete object with the so‑called genitive -n (often called the “accusative of common nouns”). You intend to empty the dishwasher completely:

Total object (complete result): Tyhjennän astianpesukoneen.
Partitive object (incomplete/ongoing/negated): En tyhjennä astianpesukonetta.

How is the compound astianpesukoneen built?

It’s a three-part compound:

astia (dish) → genitive linking form astian (of dishes)
pesu (washing) → astianpesu (dishwashing)
kone (machine) → astianpesukone (dishwashing machine)
As a total object, add genitive -n to the whole compound: astianpesukone
- n → spelled astianpesukoneen (the final e lengthens: kone → koneen).

Why is it astiat and not astioita?

astiat is nominative plural and here functions as a total object: the whole set of dishes (the dishes).
astioita is partitive plural and would mean some dishes or an indefinite amount. Examples:
Laitan astiat hyllylle. (I’ll put the dishes—presumably all of them—onto the shelf.)
Laitan astioita hyllylle. (I’m putting some dishes onto the shelf.)

What case is hyllylle, and why that case here?

hyllylle is the allative case (-lle), meaning onto a surface or to someone/something. Use it for movement onto a surface:

pöydälle onto the table, hyllylle onto the shelf If you move something into an enclosed space, use the illative (e.g., kaappiin into the cupboard). Hyllyyn (into the shelf) would be odd unless you’re literally putting something inside a hole in the shelf.

Can myöhemmin go somewhere else in the sentence?

Yes. Common options:

Myöhemmin tyhjennän astianpesukoneen ja laitan astiat hyllylle.
Tyhjennän astianpesukoneen myöhemmin ja laitan astiat hyllylle.
Tyhjennän myöhemmin astianpesukoneen ja laitan astiat hyllylle. Placement changes emphasis more than meaning.

Does myöhemmin apply to both actions or just the first?

By default readers will understand both actions happen later. To be crystal clear you can add sitten:

Tyhjennän astianpesukoneen myöhemmin ja sitten laitan astiat hyllylle. If only the first action is later, rephrase:
Tyhjennän astianpesukoneen myöhemmin, mutta laitan astiat hyllylle nyt.

Why is the subject pronoun missing?

Finnish verb endings show the person, so minä is optional. Tyhjennän and laitan already mean I empty/I put. Include Minä for emphasis or contrast: Minä tyhjennän…, en sinä.

How would I say I’m in the middle of emptying (not necessarily finishing) the dishwasher?

Two natural options:

Use an inessive action construction: Olen tyhjentämässä astianpesukonetta. (I’m in the process of emptying the dishwasher.)
Use a partitive object to show an ongoing/incomplete action: Tyhjennän astianpesukonetta.

Could I use a different word for dishwasher, like in everyday speech?

Yes. Colloquially tiskikone is very common:

Tyhjennän tiskikoneen myöhemmin… Be careful with pesukone (usually the washing machine for clothes). Astianpesukone is the unambiguous standard term.

Is laittaa the only way to say put? What about panna?

laittaa is the safest, most general everyday choice for put/place.
panna is also common but can carry a sexual slang meaning in some contexts; many learners prefer laittaa to avoid ambiguity.
More formal/precise verbs exist: asettaa (to set/place carefully), siirtää (to move), nostaa (to lift onto).

Any pronunciation tips for tricky parts like tyhjennän, myöhemmin, koneen, hyllylle?

tyhjennän: pronounce the hj as an audible h + yod; the nn is long: tyh-ye-nnän.
myöhemmin: both m’s are geminated (long); y/ö are front rounded vowels.
koneen: the ee is long: ko-neen.
hyllylle: both l’s are long; y is a front rounded vowel (lips rounded, tongue forward).