I've also heard there's a specific brand from Home Depot that many people use, but I can't remember the name. I've been using an epoxy putty from Ace hardware. I can't remember exactly what it's called, but I believe it's the only Ace brand epoxy putty that's waterproof. It's a blue stick, but it cures white. I think the big things to look for are that it's waterproof, cures under water, and does not have any metals added to it. There are quite a few that have metal in the epoxy, but it seems to be pretty clearly stated on either the front or back of the package.