Problem scenario
You want to prevent gnats from living and reproducing in your home. What should you do to keep fruit flies or gnats away from your home?
Solution
1. Buy a trash can with a foot pedal for your kitchen. These are convenient, and keep gnats from flying in the trash and out to your kitchen.
2. Pour boiling water down the drains (e.g., bathtub, bathroom sink, kitchen sink), once per week. The larvae can reproduce by living in the drain. The toilet does not work as a place for the larvae. The boiling water will kill the eggs.
3. Don't leave food out (e.g., fruit or leftovers). Clean dirty dishes immediately.
4. Fix plumbing leaks quickly. Sometimes an angle joint is old and needs to be replaced. Sometimes an entire faucet or a garbage disposal needs to be replaced. You may need to tighten a pipe.
5. Do not overwater indoor plants or let a puddle of water sit.
6. A trap of vinegar, dishsoap and sugar in a bowl can help. The sugar helps draw them in; the dishsoap prevents them from flying out; the vinegar dissolves their bodies. The sugar is not always necessary to attract them. In California the gnats are usually slow flyers, but even southeastern gnats that fly vigorously can get trapped in the vinegar and dishsoap. You may want to see this article for more information.