My New 72"x20"x20" Tank Build

[GreenSpottedPuffer]

Ok, back to the tank!

I filled the tank with about 10G of water this morning but had to stop. Seems that the overflow has a slow leak near the bottom, so when I add water tot he tank it gets into the overflow a little. This is obviously a problem.

My question is, do I need to get the water back out completely to add more silicone to the overflow or can it be done wet? Im guessing it all has to come out.