@pkouzm since you do not have a good way of getting to that damaged tank, other than a small opening, this will be difficult. Most Likely nothing is going to be 100% perfectly sealing it. What feels to your wife as a "feels like a a tiny knob" is most likely the polyethylene "cauliflowering" to the outside from the damage with the drill bit. If anything, I would try a product like Flexseal Tape. I am usually very pessimistic with any of those products, but in your case you do not have very many options. Clean it as good as you can, a bit of rough sanding and then apply the tape over the hole. Follow the manufacturers directions of course ;-). You might even try a small patch then a bigger patch and going bigger again. I do wish you the best of luck and no matter how you fix it, do let us know how it works out for you.