Get Rid of Fruit Flies for Good by Treating the Drains, Not Just the Fruit

The Problem

The trap catches a cupful, the fruit goes in the fridge, and a week later the fruit flies are back — because the flies were never mainly about the fruit. They come for yeast growing through fermentation, one female lays around 500 eggs that hatch in about a week, and the biggest fermentation source in the house is the biofilm inside your drains.

The Technique

Hit all three fronts at once:

1. Cut off the food. Cover the fruit bowl with mesh, and clean the sink — including the sponge, which they can lay eggs in.
2. Trap the adults. Mix apple cider vinegar, beer, and a piece of ripe banana in a cup — fermentation aromas are the draw — and add a splash of dish soap so landing flies sink. Rub a sheet of plastic wrap with the ripe banana, stretch it over the cup banana-side down, poke holes in it with a pen tip, and let it sit out a few days.
3. Clean the drains. Pour enzyme cleaner into every drain in the house — kitchen sink, bathroom sinks, shower — and leave it overnight. The enzymes and bacteria eat the fermenting gunk that was breeding the next generation.

Steps one and two handle this week's flies; step three is the one that ends the cycle.