How does a cell regulate what leaves its vacuole?
Your question is not entirely clear, even after the edit. However, I believe it's worth mentioning that the vacuole, just like any other membranar organelle1, is surrounded by a biomembrane.

Such biomembranes have transport proteins, which can be channels, carriers or pumps, and those transport proteins can determine which substances will get in/out of the vacuole, either down the electrochemical gradient (channels and carriers) or independent2 of it (pumps).

Here is a diagram showing the membrane of the vacuole with some transport proteins:

 

Therefore, since the cell can open or close a give gate or activate/deactivate a given pump (just like the transport proteins in the plasma membrane), that helps to explain how the cell decides what gets in or goes out the vacuolar lumen.

1: Unfortunately, there is not a consensus around the definition of organelle. The definition I use states that all organelles have a surrounding membrane (therefore, a ribosome is not an organelle), which renders the expression membranar organelle pleonastic.

2: It's very common reading that pumps will transport the substance against the electrochemical gradient. That's not correct. They will transport the substance independent of the gradient, that is, they can pump a substance against the gradient or down the gradient.