Technique?
Depends on you - if you're using standard caulking tubes like the kind that load into a gun one should more than suffice unless you're one of those folks that likes to run the bead an inch above and below the seam and really thick. Am a less is more type myself and lay down beads slightly larger than a pencil and then use a a finger run the length of each side in a single stroke to spread the caulk. If you're using smaller squeeze tubes of sealant I'd guess 8 oz. would do the job (my way) and a lot more using the old school style.
The real key is getting the surface clean so the sealant bonds well. The water pressure will push the sealant into the seam but if there's oil or some such between the glass and the sealant the pressure will also push the water through anywhere where it didn't stick. I use isopropyl alcohol and a clean cotton rag for this and run a hair dryer around the bottom for a couple minutes just to eliminate any residual moisture.
Luck, and open a window unless you want a silicone buzz. Upon reflection Jason has a point - why try and save a couple bucks being miserly on silicone when it's only the most critical part of the whole set-up? I rarely have substrate more than 1/2" deep and hate seeing sealant in the bottom and corners of tanks so I'm very minimalist in application, but if you haven't done a lot/any of these before probably better to be rather a bit more than less generous with the sealant.
Congrats again on the tank - lots of fun ahead.