Article in English: A duster bulb will enable you to apply a thin layer of boric acid. Squeeze the bulb to puff a small layer of powder along the floor and walls in your kitchen and bathroom. The layer should be barely visible to your eye. Do not apply too much boric acid. If you do, then the roaches will be able to detect it and they will avoid the area.  Do not use a spoon to apply the boric acid. You can purchase the acid from your local hardware store. Do not apply the acid on countertops, especially where food is prepared. Drill a hole in your drywall big enough to fit the tip of the duster bulb. Place the tip of the duster bulb into the hole. Squeeze the bulb to dispense the boric acid in between your walls. Since roaches tend to live in between walls, this is an effective way to kill them. But do not use it in combination with sticky traps. The traps will prevent the roaches from going back home, which helps spread the acid to other roaches.

Summary in Vietnamese:
Dùng quả bóp cao su để phun axit boric. Phun axit boric vào giữa các bức tường. Kết hợp phương pháp này với bả gel và hộp bả, nhưng không dùng kết hợp với bẫy dính.