[Carl n Susan]

The gasket has a grove (for lack of a better name) around its edge. There is a corresponding edge protruding from the toilet. Getting the gasket seated was a challenge for me. But once I got is seated properly, it was centered in the hole.

If your holds water, let it go and see for how long. I bet it will drain a couple of hours. Not what you want.

The tip I was given was to let the ball valve close and then insert the gasket, working it into position. Good luck!