I was just wondering about if a seal was needed on those buckets.
If you mean a sealed top on buckets with nipples in the bottom, the answer is a resounding NO! In fact, if they are sealed the water CAN'T come out of the nipples, it creates a vacuum. It is the opposite of the waterers that have a "jar" type top and a screw on base with a small hole in one place (and the similar 2 part galvanized waterers). Those work because the vacuum keeps the water in. Water stops draining into the rim when the water covers the top of the hole. As the birds drink or the water evaporates, the hole is exposed and more air gets in letting the water out until the hole is covered again. If you get a hole in the top of one of those, the water will all drain out immediately because the vacuum is broken.
Bruce