How can you repair a cracked ejector pit?

Well, it sounds like the best way to go and if it took 15 minutes for the level to drop half way it must be a small hole. I agree that you would have a hard time replacing the hole thing. I'd look into a silicone that would stick to the bottom of the pit also you might contact a swimming pool store, they have glues that work under water. But I'd do what you may be thinking and that is to clean it totally out & dry it before using a patch or silicone. Good luck.