Tortoises that get regulair soaks will get rid of the water they hold in their bodies. And then drink to get fresh available water.
In nature they can hold their water for a long periode of time. Cause there is not always fresh water available.
My Stars do it every time they soak, so every day.
I would soak your Tortoise for at least 30 minutes or more. And change the water when it gets dirty. You want your Tortoise to be healthy. So it takes some work. *glimlach*