There are several ways to kill gnats, depending on the type of gnat and the severity of the infestation. Here are some methods:

• Vinegar trap: Place a bowl near the infestation and fill it with vinegar before adding a teaspoon of plain sugar, which is what the gnats will be drawn to.
• Apple cider vinegar trap: In a small bowl, mix a half cup of warm water plus two tablespoons of apple cider vinegar, a tablespoon of sugar, and about six drops of liquid dish soap. The sugar will attract the gnats, the dish soap will prevent them from escaping, and the vinegar will kill them.
• Wine trap: Pour some stale wine into a small vessel, add in a couple drops of dish soap, then place the mixture in gnat-filled areas of your home and wait for the bugs to drown in the mixture.
• Boiling water: Pour boiling water down your drain to kill any eggs in your drain by pouring boiling water in the sink. Kitchen sink drains are common spots where gnats lay eggs, especially in garbage disposals.
• Bleach or hydrogen peroxide: In order to get rid of drain gnats, pour a half cup of hydrogen peroxide or bleach in the drain.
• Insecticidal spray: Use an insecticidal spray made for indoor use.
• Diatomaceous earth: Sprinkle diatomaceous earth over the dry soil in your plants. It will trap the gnats until they die from dehydration.
• Bti drench: Drop a mosquito dunk labeled as safe for use around pets and wildlife in a watering can or bucket. Let it sit long enough for the dunk to release its insect-killing bacteria into the water. Pour the water over the soil of your outdoor plants.

Its important to identify the type of gnat before attempting to kill them, as different types may require different elimination tactics.