With 3/4 inch you should be able to make a decent joint with solvent. Tricky though to get 0 bubbles. 40/42 is best for material over 1" IMO but can certainly be used for 3/4" although a more complex process than solvent i.e methylene chloride/acetic acid (vinegar).
Much more to this process than meets the eye. Annealing? recommended but not always necessary depending on quality of machining IME. Of primary importance is joint width, too much and you will get an exothermic reaction as the cement boils. Although bubbles can be formed when mixing they also mysteriously appear if too much cement is used due to a quicker reaction and more heat being generated. Too thin of a gap and you wont get the right bond strength or worse a dry joint as it shrinks during curing.
I've had luck with up to 1/4 of an inch gap. Posted pictures of a similar tank on Silent Bobs thread. Remember this stuff shrinks as it drys and too much uncontrolled shrinkage will result in creases in the joint. You have to monitor it as it drys, I use screw jacks made with long sections of threaded rod and give them a turn every few minutes to pull the panels together. This is to ensure no creases take place and the cement level remains above the surface of the panels. Do not add more cement as it is curing the reaction has reached a different stage and adding more will only produce a weaker joint. Similar to a monolithic concrete pour vs layers.
So much more to the process than this, but to prevent long winded posts I'll try to answer any questions as they are asked. Wednesday has some great advice on the use of 40/42 as well and knows what he is talking about.
Keep in mind after the joint is overfilled and the cement is dry you will need to take it down to the same plane/surface as the existing material. I use a hand router along an edge with a 1/2" 3 flute spiral down cut bit (Onsurud # 60-250) to trim down to about 1/16th and then finish with a micromesh kit. Sand in 90 degree angles keeping in mind when you sand the seam down to the surface of the base material you want to end up with a very fine grit. Too course at this point and you have groves left by the sand paper in your cement seam. Trying to remove it will produce a concave surface along the entire seam that will distort the view after trying to sand out the heavy groves produced by to course a grit. Your aiming for an invisible seam so make sure you end up with a smooth seam before you get to the base material. Novis 1 and 2 to finish up in a circular pattern after finishing with 6K grit wet.
This is greatly abbreviated and Im leaving out a lot. If you have any questions ask away, Im sure Wednesday or I should be able to fill in the gaps (no pun intended).
We can discuss annealing or the shape of the edges if you want, a couple options depending on what your trying to achieve, strength, clairity or a little of both, it's always a trade off and much of this depends upon the height of the tank.
