I can't speak to the difference between RTV and AGA silicone, because I don't know anything about the AGA. The RTV differs from the silicone you get at HD or Lowes in that the RTV is adhesive and HD or Lowes silicone is a sealant. The bond between the glass and silicone is much stronger.
This was my first tank and I laid a bead of RTV down and set the glass into it. I pressed it together but not with a lot of pressure. And then clampped it in place using enough force to hold it but not really squeezing it to force out more RTV. I didn't even clamp the sides to the bottom, but used aluminum foil tape to hold it in place. The foil tape grips well and doesn't stretch. Then I used the corner clamps at the top and the 2 long clamps at the to hold the sides in place. So to answer your question, no, I didn't try to squeeze all the RTV. It seems to have ended up a pretty tight fit, meaning I haven't tried it, but I'd bet it wouldn't be too easy to get a razor blade between the pieces of glass in this tank either. I then did a bead along the inside of each seam.
I seem to remember reading somewhere, or maybe it was a club meeting with a custom tank builder, but somebody was laying the bead of RTV down and then laying a fine monofiliment fishing line in the center of the bead before they set the glass together, preventing the weight of the glass from pushing all the RTV out. I haven't tried that... yet. Also I've heard of doing a double bottom. Say you are using 3/8" glass and cut the bottom for a 2'X4' tank. Then use a second sheet of glass cut 3/4" shorter in both directions. Center the smaller glass on the bigger glass and you have a 3/8" dropped rim to set your 3/8" side glass up against. That gives you very well fit corners with way less fuss getting things lined up AND gives you a 90 degree corner to RTV the glass into which will be much stronger. I did consider making the bottom glass 1/4" bigger in each direction which would make a 1/8" 'lip' that would stick out from under the sides. That could be an out side the tank extra bead of RTV, but I didn't do it and I don't think on a shallow frag tank it's a big deal.
BTW, I added a coast to coast weir (overflow) and cut the top with a single shallow 'V' from one side to the other, rather than the traditional teeth. The flow over the shallow V works very nicely but I had the tank set up too deep, so I needed to lower the overflow wall. I got out my belt sander with some 80 grit and sanded down the weir by 1/4" and made the center of the V a bit deeper. I have to admit, I was concerned about creating a leak somewhere in the RTV with all the vibration of the belt sander. But it wasn't an issue. The new frag tank is set up and full of coral and doing fine.
