Gnats in the Bathroom

The best thing I find that is working for me is fill a small bowl, like a pyrex glass bowl with water and dish soap and stir it to distribute the soap. I have tried the vinegar and soap and that didn't work at all. I also pour bleach down the drains. I did buy and hang up fly paper and that really worked. I had a horrible amount of them and I think now they are finally starting to go away. It takes a while. They breed in the drains, so the bleach really helps. Pouring hot water down the drains works somewhat if you do it monthly.

You might be dealing with sewer gnats/drain flies. They can set up housekeeping in floor and sink drains.

First I'd try slowly pouring a half gallon of boiling water down every drain in the room. Don't pour it too fast - you want some water to remain in the trap (elbow joint).

Repeat the boiling water treatment for a few days in a row. If these are drain flies (which it sounds like they are, since most gnats wouldn't hang out in the bathroom), this should solve the problem. There are also drain products you can buy that are made specifically to get rid of sewer gnats.

For good, not much. They are territorial and come to where they can find the scents they love.
You can however, kill them. Fill a plastic cup half full of apple cider vinegar and a couple drops of dish washing liquid. That breaks up the surface adhesion and they dive in and drown. If you can, put it up high light the top of a cabinet or somewhere you don't have to see them or knock it over.

I've heard that spraying Listerine will help. It can't hurt, to spray the fixtures, and around the sink, there are many different "flavors" now.