That the Sage himself used the Eighth Gate to beat the complete Juubi, and by escaping the initial escape of death, he sealed it into himself? I mean, considering the massive amount of life force the body itself holds.
I think he got the sage tools after becoming the Juubi's host because Madara puked out his tools after he became the host.lol why not? But I'm thinking he used his sage tools and powerful body to beat him.