BillD is absolutely correct about the silicone between the glass, the edge or butt seal, holding the tank together. I don't know what or why I said to the contrary. I think I confused myself and lost track of what I was trying to say. Which, I think is: Sometimes, with luck, a small void in the butt seal can be sealed with a wider and longer fillet or flanged seal over existing inner fillet. Note the "sometimes" and "SMALL void." As everyone has said new silicone over old cured silicone is not recommended. but sometimes for some reason it does grab. In the case of a void we are relying on the rest of the butt seal to hold everything together, and that brings me to filling a tank in stages.
First that's the way Dr.s Innes and Axelrod said to do it. Of course that's like doing something because Granpappy did it that way, but if two such authorities, with their well known long standing fued both agree on something, I'm not gonna argue with either of them. Now you might save some water filling in stages, the main reason, given by both of them is in case a seal does give way resulting in a catastrophic failure and possible broken glass. I have seen it happen to a new tank that had been sitting full for a couple of hoursand a few times in repaired ones.. The complete filling of a tank, especially a large one, and especially with water that is appreciably warmer or cooler than the glass, causes somewhat sudden stresses in the glass. Usually the seal gives way but I saw the front glass of a 100 gal
tank crack, luckily it wasn't mine and I wasn't filling it. So I play it safe, especially when a tank is in its permanent place.,Stress on thicker glass of larger tanks is more than on thinner which can bow and flex a bit easier B4 cracking.