The tomatoes are the direct object of the sentence, hence in accusative plural: die Tomaten.

den Tomaten is dative plural.

That would generally involve a brush or some other tool, whereas waschen might just be holding them under running water and perhaps rubbing them with your hand.

abwaschen is basically "do the dishes; do the washing up" and doesn't generally take an object.

(Though there's also abwaschen with the sense "to wash something (e.g. dirt) off from something else", e.g. den Schmutz [von den Tomaten] abwaschen. But here, the tomatoes are not being washed away from the surface of something else, so abwaschen isn't appropriate, in my opinion.)

It is a correct German sentence but not a correct translation of the English sentence.

The English sentence has "the tomatoes" (a specific group of tomatoes) and not "tomatoes" (tomatoes in general). The German translation should have die Tomaten and not just Tomaten.