I need to seal a chicken watering fount so that it won't let air leak in, allowing the water to dribble out. This requires coating the interior of a galvanized steel cylinder, about 8 inches across and 18 inches high, with something that will plug pinhole leaks and joints and will not leach unhealthy chemicals into the water.

The expert advice I found was to paint the surface with silicone aquarium caulk, using a foam brush. However, I'm skeptical that anything called "caulk" would be thin enough to spread with a brush.

If you have experience with silicone caulk, particularly aquarium caulk, what do you think? Will any such product work, or do I have to get a certain brand, or is this just a hopeless idea?