Grey Water tank leakage

[JohnGreydanus]

Thank you for the posts of past years on hairline cracks in the GW tank.
We incurred one now also.
I've used two layers of Medium Black ABS cement.
It did not truly fix the problem but helped somewhat.
My wife then told me she had purchased Flex tape.
I placed that on the crack, which is in the center of the rib in the middle of the tank, as well as by the out take. Yep, two leaks in one trip. No clue why.
Anyway, I read that one should drill a small (HOW SMALL?) hole at the start and a hole at the end of the crack. Would that not make the sepage worse if the cement or the flex tape do not fix the problem.
Also, I read about 'welding' the crack. What exactly is meant by 'welding.'

So, at the point in time I wonder if I should take off the flex tape AND scrape of the cement to the best of my ability and start over.

Any good suggestions from you who know more than I do on this, and I don't know too much, would be greatly appreciated.

Thank you so much.
John G.