Jill,
I may have given you wrong advice about how the thing is mounted to the tank. This thread jogged something and I sort of remember comments about some valves being screwed in. Hayward uses a collar that grabs the valve and tank lips and pulls them together.
As for the valve blowing out that is quite possible. Consider the tank pressure and the number of square inches on the valve and you can one heck of a force trying to push it out of the tank. Because of the pressure the tank expands a little with the pump on and because of this I can't see how any bond or glue will hold. Hope someone has some ideas for you all.
Al