I applied a high-pressure plastic sealant inside a cracked and leaking toilet tank. It sealed it completely. Due to the material's elasticity, it has not had any issues with the weight of the water, nor have I experienced any problems with expansion and contraction due to temperature changes.
I applied it with a brush, two coats, with a 24-hour interval between applications. I let the material "mature" for an additional 48 hours and the result was impeccable.

I wouldn't expect anything less from an American product. Excellent! I've been searching for years to find "something" to repair a hole in a polyester sink BEFORE I THROW IT away in a construction dumpster. I've tried everything that exists and doesn't exist in the Greek market. And I found it. The color bothers me a bit, the importer could have it in other shades, since they exist, but who cares. ABSOLUTE WATERPROOFING, ABSOLUTE ADHESION, absolute product. I highly recommend it (not suitable for roofs, be careful!).