duct tape...fixes everything... thats what the one glass company told me you get a crack in your tank duct tape it it will hold the water until you can deal with it... needless to say i didnt order my glass from them. but it gave me an idea fro a duct tape tank i may build lol.

When they fix windshields do they repair them with silicone? No, they use epoxy!!

That is usually for a crack I think. And also tempered laminated glass

Even a windshield chip similar to what the OP is talking about it is repaired with epoxy. Silicone will probably work but myself I like the epoxy idea as being more of a permanent fix. Each to there own tho!

I use silicone on my gaskets, but not silicone glue. The glue is a pain in the but to clean off. I use silicone gel from SCUBA shops (I am a diver and so have lots around). It is food grade, inert, and keeps the seal on 3000psi orings from leaking on my scuba tanks. It also allows easy r&r if you need to replace it later and it allows for some give (it is a lubricant) to rotate your bulkhead on the tank. I have it on several connection points in my tanks that I want to seal but also may want to remove later.

Epoxy? What kind? This is just a sliver of a chunk that flaked off, not sure there's enough surface for epoxy. Or where to get it. I think silicone is probably easier, and I have it on hand.

No, I don't want to drill more than I have to, it's always stressful :) And my luck, I'd chip it again and still have to deal with it, and exchange the bulk head, get new plumbing, etc...

If its not deep I wouldn't worry about using epoxy then. Mine was on the outside of tank but I'm kinda picky so I filled it with epoxy then sanded it level. I probably could of just left it be but.... The windshield repair places use a more expensive special epoxy but I just used just regular 2 part epoxy that can used on various surfaces including glass and bought just about anywhere.

you could drill the same sized hole (without a chip) in a patch piece of glass. Silicone that to the inside of the tank and then use your bulkhead. Just be like having thicker glass is all.

Can't say I've ever drilled a hole without getting a chip in it :) Then if I have to silicone the new piece, it's just like siliconing the the chip :)