It will probably seal it, but it will be no where near as strong as if you use real PVC glue. The real stuff contains solvents and will bond the PVC together. Silicone wont.
I wouldn't take the chance since if it fails and you don't notice it, you could kill your fish. Maybe I'm just paranoid.
Agreed. Silicone is just a sticky filler. Not good for bonding. For the best results use pvc cement. Much better than 50+ gallons on the floor, ya know?
Just a piece of advice. It would be better to keep all of your questions and thoughts in one thread. That way, you can come back and reference them when you need to. I have seen at least four different threads asking similar questions. It is also more effective because everyone who reads it knows exactly what you are trying to accomplish.