On the "home remedy" side, you can mix a tablespoon of apple cider vinegar into a small bowl of water, and sit the bowl near your potted plants. You can use wine or fruit juice as well. Many a gnat has reportedly met their fate with this concoction.
Your drains are also a haven for gnats. Pour some vegetable oil down the drain; this will saturate the gnats, hindering their ability to breed.