Cut the top off a plastic bottle
Invert the top and place it into the bottle to form a funnel
Add bait such as sugar water, fruit juice, vinegar, or overripe fruit to the bottom
Tape the edges to secure the funnel in place
Make a few small holes near the top for flies to enter if needed
Place the trap where flies are common
Empty and replace the bait regularly
Dispose of trapped flies and clean the trap as needed