I'd do it just like fastrd400 said. Make sure and use acetone to clean off the old silicone. Get it all off there. And then get all the acetone off the glass. :mrgreen:
I learned this from building toy airplanes.
I use 2-part epoxy and other fiberglass or polyester resins a lot. Anytime you are messing with glue (silicone) - you better be ready with a bunch of disposable rags (paper towels) and a solvent that will wipe the glue off completely (acetone).
I would be ready with a 1/2g can of acetone and a whole roll of paper towels. Snap the paper towels off one at a time and pile up about 30 or 40 of them. Get them ready so you can just pick one up and soak it in acetone without having to mess with the roll.
I fold each paper towel up as I grab it. Takes 3 seconds to fold a towel over 4 or 5 times and make it 2" square and 3/4" thick. Just the right size to cover the hole in the acetone can. Hold it over the can and shake vigorously until the paper towel is nice and soaked. Tip the can up if you need too.
Now wring the towel out back into the can. What you have left, is a completely soaked paper towel. Takes 5 seconds to unfold it.
It helps if you have a helper. You should both wear gloves and safety glasses. The helper just soaks paper towels for you and takes used towels from you and pitches them in the trash can. The helper does all the dirty work while you make the seams nice and clean and detail the tank so no smudges of silicone end up dried on the glass where you don't want them. My wife usually helps me if I'm playing with airplanes and epoxy. Or if I'm at my friend Pete's house, we help each other when it comes to glues like this. Wipe off all the spooges and messes while they are wet.
You might have to press the top down and wipe the excess off the inside of the tank first. Then I'd probably put a big sheet of 3/4" MFB or plywood on top of the tank and stack books, bricks or some other weights all around the perimeter to put pressure all around while the silicone dries. About 200-250 pounds around that perimeter would get it stuck down really good and the glass will hold that up easily. Make sure it's level when you do this. Maybe set the tank on top of another piece of heavy plywood and level that plywood with door jam shims?
I've never done it, but I think I'd probably approach it sorta like that. Good luck and take pics!! :Cheers:
