Plumbers Epoxy dries under water, it's probably the same stuff you buy at the LFS at more of a cost. It's usually right next to AquaMend at Home Depot. Just be careful not to get the stuff in the plumbing aisle. It says it contains steel. This stuff is down were they keep the glues. I've not seen any ill effects using it, I do like AquaMend better, although it takes awhile for the white to blend into your tank's rock work.