Follow-up to my house gnat question (details inside)

I am having a terrible time with tiny flying house gnats. They are hanging around my plants. Last Winter, I brought in a bag of potting soil that had been sitting out in my Dad’s backyard. I used to the soil to top off one of my indoor plants. Bad move, as with this bag came some nasty gnats.

I tried a couple of home remedies (suggested by jellies and some that I found online); adding cinnamon to the soil, adding dish soap to some water and soaking the plants with it, having a container of vinegar (attract gnats) and dish soap (trap the gnats) near the plants. None of these things work.

The gnats are getting worse and I would really love to keep my indoor plants. The gnats are getting into my dog’s water dish and are hanging out all along my front window. I need to bring out the big guns (chemicals). Suggestions?