Okay, maybe I'm paranoid, but...if that's just a chip, I would personally remove the bulkhead, get a piece of glass large enough to act as a patch and silicone it securely in place covering the entire hole, the chip and at least a couple inches of the surrounding glass. The bulkhead would either be re-drilled and relocated, or perhaps drilled into the patch and allowed to go through that same hole if the threaded shaft is long enough.
If that little line is actually a crack, rather than just a "hair" of dried silicone pulled off during the initial installation, then I wouldn't even consider using the tank. A crack will eventually spread and result in failure, quite possibly catastrophic.