I buy Mastercraft Window and Door Silicone at Crappy Tire. It says right on the back.."Ideal for use in Aquariums,allow 2-5days before filling aquarium." Its whats holding my sump together
Its cheaper than GE brand too.. and cheap is GOOD! Oh and I find that if I leave a big dollap hanging out the end of the tube when Im done.. Then when I want to use it again, all I have to do is yank it off.. and its down to the good stuff again,