Homemade Fly Traps | syrup and vinegar Rinse out empty gallon milk/water jug. Cut multiple holes all over the jug about the size of pen caps. Do not cut any holes in the bottom 4 inches of the jug, where you will add solution. Pour 1 cup of syrup/molasses/fruit juice into container, then 1 cup of apple cider vinegar. Twist cap onto jug and place it in location where flies are heavy. Empty the jug every few days and refill, or toss the whole jug and start fresh with a new container.