As the flies go into these traps, they don't seem to be smart enough to find their way out so they are bound to drown in the water below. Near the end of this 48 second video, a total of 2 flies enter this trap.
Here's my set up. Flies slowly started coming in after I took this picture, and the one on the left, closest to the lid of the garbage can ended up catching flies at the fastest rate perhaps due to the amount of flies that fly around that one spot. It also seems like flies are more likely to go into the trap once there are already flies flying around inside the trap.
Here are a couple pictures of the disposable fly trap. This is very effective for the short term, but around a trash can, it will only last for 3 days until there are so many flies that there is no longer any room to fit any more in the trap. The top part of it can still be cut off and placed on top of a jar or one of those plastic wide mouth tropicana orange juice 1/2 gallon containers.