A plastic water bottle
A piece of 8 ½ by 11 inch paper
A 50/50 solution of honey and vinegar
First cut the top off the water bottle. Then roll up your paper to a funnel shape. Trim the bottom off so that there is a large enough hole in the bottom of the funnel for the gnats to crawl through. Make sure the funnel is wide enough to touch the edge of your water bottle at the top and long enough to go most of the way to the bottom. Then tape your funnel together in order to keep it from unrolling.
Now pour about 1 (one) tablespoon of honey/vinegar solution into the bottom of the bottle. Next, insert your funnel. To finish it off, you will need to put tape all the way around the edge of the water bottle to seal any spaces between the water bottle and the funnel.
Your gnat trap is now ready to use. Simply put it in a place where you have the most trouble. Gnats can get inside the trap, but they cannot get back out.