i would find out what glass guys use to bond there glass together in showers and such.
i dont see it being that much of a issue but in the end the main issue is the thickness of the glass. and how confident you are in it. i would brace all the way around the top and bottom of the tank as to help strengthen the entire box, simular to what you said about strengthening it from bowing. and you can make a clean caulking line doesnt have to be thick. i would use the glass bonding adhesive, and two small lines of cauking inside and outside as a extra. and would just put a clean thin line of black tape down the joint. as a finnish. anything is possible. i would just make sure to only have small fish,and would be cautious on filling the entire thing. i know about doing what you have to do sometimes. id just say go for it. just know it could fail. but thats how some of us like to learn.

just keep it over your bathtub.hey may help with any constipation issues never know, go for it!