It is bad to dispose of tampons improperly.
Dina is experiencing her time-of-the-month and knows that her school's bathroom stalls don't contain personal receptacles for trash.
Dina wants to avoid embarrassment.
Dina wraps her tampons in tissue paper and walks them over to the trash whenever leaving a bathroom stall.
Not wanting anyone to see her tossing a tampon, Dina chooses to flush her tampons whenever she uses the school bathroom.
Dina's tampons go unnoticed and the school's plumbing remains intact.
The school's plumbing gets clogged up, putting the bathrooms out of order for a few days.