greatest thing since indoor plumbing

the greatest thing since indoor plumbing

A humorous and hyperbolic statement indicating one's belief that something is excellent, especially something new and innovative. These waterproof jeans are the greatest thing since indoor plumbing. I don't have to worry about getting soaked!

greatest thing since indoor plumbing

 and the greatest thing since sliced bread
Rur. the most wonderful invention or useful item in a long time. As far as I'm concerned, this new food processor is the greatest thing since indoor plumbing. Joe thinks Sally is the greatest thing since sliced bread. You can tell just by the way he looks at her.