How are marine glues and epoxies rated when it comes to the pressure they hold?

I mean, when they figure that the stuff could contain a certain amount of water, what unit of measurement do they use?





I have a 150 gallon tank, 4'x2'x30".



What is a good sealant to use when putting in the overflow panes on the inside of the tank, where it's drilled? 3M Marine Grade Silicone Sealant? It does say that it will bond to glass, but will it really hold back 150 gallons worth of pressure from seeping through? If not, do you all know of anything that could easily do it?