Here are some solutions to your question.
Sandy: maybe this will help
My favorite way is to mix some old red wine or red wine vinegar with sugar and a few drops of Dawn into a canning jar. I then put a piece of plastic wrap on the top and poke holes in it - big enough for the gnats. Once they fly in to the sugar sweetened vinegar, they will die. I've seen my local outdoor veggie market do the same thing. I hope that helps. Wishing you the best.
The treatment is pretty much the same as you'd do for fruit flies.
They are probably living in your sink drain, to get rid of them put 1/2 cup baking soda followed by 1 cup white vinegar, when the fizzing stops flush the drain with hot water. You might want to close the drain after that.
For the airborne ones, you can do the vinegar in a cup covered by plastic with a hole as others have suggested. The method that works for us is a mouse sticky pad ( multipack at Walmart). Open 1 up and lay it flat, put a piece of decaying sweet fruit on it. That will draw the gnats, they land on it and that is the end of them.
Vinegar does indeed work well for us. I use a small mason jar, jam size, fill the jar about 3/4 the way full, poke about 10 holes in the lid of the jar (I use a hammer & nail) screw the lid on and place the jar or jars where you need them. Hope this helps!
Use some foaming drain cleaner in all your drains.
This should help:
The vinegar trap in the covered glass jar a cup has always worked for me.
Per link below
Pour just enough cider vinegar to cover the bottom of the jar. Add a drop of dish soap (it will break the surface tension of the vinegar so the fruit flies can't just sit atop the liquid). Now, cover the jar with plastic wrap and poke a few holes in the top.”
Hi Sandy: Yick! Hate them :( Here's a site that should help: https://www.organiclesson.com/6-ways-to-instantly-get-rid-of-gnats-at-home/
A half cup of warm water plus two tablespoons of apple cider vinegar, a tablespoon of sugar, and about six drops of liquid dish soap just might be able to cure your gnat woes. They'll be lured in by the sugary mixture, but once they dip in for a drink, the sticky dish soap will trap them.
This might help: Fruit Fly Trap
You can make a fruit fly trap. Cut a plastic bottle about 2/3 of the way up. Remove the screw top lid. Squirt a little dish soap in the bottom, add 2 Tbsp apple cider vinegar, 1 Tbsp sugar, 1/2 cup warm water (dissolve the sugar). Place the top inverted into the bottom. They will fly into the neck to get at the solution but won't be able to escape.
They want the water get a small bowl fill with 2 tablespoons of applecidar vinager and 2 squirts of dish soap in the middle of the cider leave like that and put it on the floor under the toilet for a week then replace mixture.that will kill them they drink it and die.
You might try something like this... https://www.homeroad.net/2015/10/a-fruit-fly-trap-that-works.html