I use the 5 gallon waterers and they are basically a sealed system with a screw on lid Never had a problem with mosquitoes, though they are in everything else that will hold a teaspoonful of water. Thank God for Dragonflies, and Backwoods Off.
This is a pretty old topic but I have a question about the guppies and gold fish, becuase I have a 50gallon rain barrel that provides water through a tube and out those little waterers that they peck at. What about the fish poop? Thats my only question.