Learn Swedish: Jag kastar inte bort den där sopsäcken. - I am not throwing away that trash bag.

In Swedish, negative words like inte usually go directly after the first verb. Because kastar bort is a particle verb, the two words get split up by inte. The pattern is: Verb + inte + Particle.

Where does the spoken stress fall in the phrase kastar bort?

In Swedish particle verbs, the stress always lands heavily on the particle, not the verb! To sound natural, you should put your emphasis on bort rather than kastar.

Why do we use bort here instead of borta?

Bort shows motion or direction (like throwing something away), while borta shows a static location (like being away from home or gone). Since throwing is an action involving movement, we use bort.

Why does sopsäcken end with the definite -en if we already said den där (that)?

This is the Swedish "double definite" rule. Whenever you use a pointing phrase like den här (this) or den där (that), the noun that follows must also be in its definite form. You are literally saying "that there the-trash-bag".