I clean tanks by fine peening but, this will not get the liner out.
I have advised so many painters on how to test a tank before paint, all you have to do is attach a air line to at tank and have about 2 psi going in and submerge it in a tank of water. Any bubbles, then you have holes. If a small hole, drill it until clean and braze. Big holes, cut out and put a plate from the inside. Weld a rod to the plate so, that you can pull it while you weld.