Overflow problems. Need help

[BMahura]

Hey everybody.
I have a slight problem in my tank right now.
a pod or bristle worm has managed to make a hole in the silicone sealent that is holding the overflow glass in the tank. When i was doing a water change i usually drain all the water from my overflow because lots of crap gets stuck in their. I relized that my tank level was slowly decreasing and i had no idea why. I then saw the hole in the over flow. I have all my plumbing set up so that if the power were to go out the overflow would drain and thats it, However now im worried (especially with all the lighting in Calgary lately) that if the power were to go out and im not home my tank would be half drained by the the time i could get to it. Im not sure how to go about filling the hole but i would like to get it done asap. Any suggestions or ways to fix this problem would be great!
Thanks
Brett