Hi! as yall just revived this old thread, I'd like to tell what I was told by an ag. student about using vinegar/sour milk for fowl. It seems that these cultures create enough acidity to keep salmonella from taking hold and sickening the stock. Personally, we don't routinely add vinegar to their water, but in hot humid weather and other times of stress, we do. We also rinse the incubator with a stronger concentration, and use a bit in the humidifying tray and also as a hatching egg dip, before placing the eggs in the incubator. As we've not had rotteness after starting this, we've decided to continue using it.
There are times we substitute lemon juice for vinegar in the water also.. when we hear of viruses going around.