@Discretepete2676, the beer drowned quite a few gnats for me. It also drowned one of those bugs that have pincers on their ass (don't know what they are called in English). Just don't forget to add a few drops of dish washing soap in the beer - this will break its surface tension and will drown the bugs easier.
Potatoes work for drawing the gnat larvae out of the soil. Luckily, in my case I didn't have any.
Best of luck with your beer/potato project. While you are at it, you may cook some french fries and down them with some beer, lol.