I had leaky stock tanks too. Be careful with Silicone on those tanks. It doesnt adhere well to plastic over time. If the drip comes back, here's my two cents from recent similar trouble........Go to west marine and get some MarineTEX. Get the bigger box because its good to have (shell out the $45, its worth it). Go home, drain your tank, apply it EVERYWHERE and let it sit for 3 hours. You'll be good to go. If you have a small drop around the threaded fittings, there's another product in the same isle, its a green marine epoxy stick (about $20) that you can apply under water and hardens overnight. Both work great and have been awesome with my stock tanks.
I hope your silicone works, but if it fails, try this.
good luck