Who knew? Pipi holo ka'au.
Here is some research. In 'Olelo No'eau: Hawaiian Proverbs and Poetical Sayings, Bernice Pauahi Bishop Museum Special Publication No. 71, copyright 1983, Mary Pukui writes on Page 291, #2658:
Pīpī holo ka'au means "It is sprinkled, the tale has fled." She says "This is used at the end of a tale to indicate that it is finished."
There are literally thousands of poetical sayings in every language. This may be a traditional ending to storytelling in various regions of the Islands. Tammy Baker of the University of Hawaii Manoa says that her family would, as a tradition, express this at the end of every tale.
I do not know if this is a common expression; I have never heard it before. But if you studied Hawaiian at Kamehameha or UH, maybe you have. Is this a common expression, and if you have heard it before, from what region did you learn it? Mahalo.