Recently our house has been overrun with gnats. I followed all your suggestions, nothing worked. I finally called an exterminator, he couldn't come but he told us to pour scalding water down every drain in our house and follow it up with bleach.
Another thing that works and doesn't hurt your plastic pipes or fittings the way bleach can is to mix equal parts of white vinegar and hot water and pour it in the drain. Occasionally throw some lemon slices in your garbage disposal with the peel and grind them up for a deeper cleaning.
To get rid of the ones flying around, just take an empty water bottle and put about 1/2 inch of white vinegar in it and leave it with the cap off by the sink. They will fly down into it, drink the vinegar and fall into it. It works really well without the chemicals.
This is great! Thanks. I have a gray water drain and don't want to pour bleach down it, and the tip of the vinegar in the water bottle is priceless to me. I am so thankful BJ brought this to us, as I am in mid MO too, and the gnats are really a problem. I have never remembered much of a problem with them before this.
Be VERY careful using the bleach. I did that when we lived in Korea (to get rid of bugs) and the bleach fumes made me ill for several days. Bleach works wonders, just be sure not to breathe in the fumes.
I wish that I would have seen this post as I had a problem with gnats about 2 years ago and no matter what I could not get rid of them. I just kept trying everything that was suggested and still no luck. It got so bad I had turned to spray bug spray such as fly spray but that does not really work. It only kills the ones that you spray. I finally found something that does work after hours of research trial and error. You take a piece of fruit or vegetable. The older the better. You cut it up and put it on a cookie sheet. Before you go to bed that night place the sheet in your oven and leave the oven door wide open all night long. When you get up in the morning shut the oven door with the food and the sheet inside and turn it on until it reaches 350 then turn off your oven. When it cools, open the oven, remove the cookie sheet and wipe out your oven. Throw away the food and wash the sheet.
I would recommend keeping that sheet separate to use only for this. I would never use it to cook on again. Then wash out your oven with a little soap and water. What happens is all the gnats will go to the oven to eat the food you left for them. When you get up in the morning they should all be in there. When you turn on the oven the heat kills them. I did this once and it got rid of all the gnats. I don't know if you will have to do it more than once or not. I have told friends to do this as well and it worked for them on the first try as well as it did for me. I wish that I could remember where I found this tip so I could give credit because it is so simple and works so well. It is much safer then the bleach as well.
I live in So. California and have had gnat problems for 3 years starting at this time of the year, every year. I use scalding water and bleach every 2-3 weeks and it really works. Where do these gnats come from? They are so annoying. I also changed the soil in my house plants. I bake the soil before I use it and it controls the gnats that tend to live in the plants.
This works for me, and it has no fumes or harmful side effects (except for gnats). Put a layer of sand on top of the potting soil on all of your indoor plants. This will smother the gnats, and it kills any future generations. You can even color coordinate it if you want. Craft shops and pet stores are the best places to find it. And terrarium sand will also work quite well. It won't kill the ones that are flying around now, but it will stop any new ones.
Cee Cee W's recommendation works very well and doesn't adversely affect humans and our environment.
Pouring liquid as poisonous and environmentally unfriendly as bleach down the drains to control bugs is the very worst advice ever. Bleach is never necessary and shouldn't even be purchased much less used and it certainly shouldn't ever be put down the drains. For any reason! Those of you who think it's OK are the reason we have a polluted earth now. Get educated and stop thinking life can be done the easy way. This is everyone's earth and it's time you all started having a little respect for it and started treating it right. For a start, that means NEVER using chlorine.