Natural Gnat Killer This works great! I used the recipe in small condiment dishes near my kitchen sink and near both bathroom sinks. I added an extra in my living room on the fireplace hearth. We could not believe just how many gnats we attracted! What you will need: 1 small jar or bowl 1/3 cup apple cider vinegar 2 Tbs. water 1 drop of mild liquid dish washing detergent such as Dawn. Instructions: 1. Pour apple cider vinegar into the jar/bowl. 2. Add water then add just one drop of mild liquid dish detergent. 3. Set the mixture in the area where gnats are a problem. 4. The gnats are naturally attracted to the vinegar and the drop of soap kills them.