When you waltz through something, you get through it very easily.
The waltz is a dance.
Examples: The Indians thought they would waltz through to the Super Eight.
When you say that something is a waltz, what you mean is that it is very easy to do.
Examples: The Indians thought that the game against Bangladesh would be a waltz. * “We thought watering the garden would be a waltz. But it turned out to be real hard work”.