Vanilla Essence: Pour several drops of vanilla essence on a couple of cotton wools. Toss the cotton wools inside the confined spaces nearest your trash can. Leave them for several days and you will notice that the area smells nice, or at least smells nicer.
Mint Extract: If you favor neither the smell of citrus nor vanilla, you can perhaps use mint extract instead. Pour several drops of mint extract on a couple of cotton wools. Toss the cotton wools inside the confined space and leave them for a couple of days.