While I'm assuming you mean the former, in the Scene where anything goes, it's usually a good idea to be specific.
I don't receive GS, but you nailed it on the head with your comment regarding taste. How nice/evil does the pee-er want to be? Is this reward, punishment, humiliation? Is this the first time the pee-ie is receiving a GS, or is s/he an experienced veteran?
Given these variables and whatever the resulting potential objective might be, I'd say your "ideal" fluid could be anything from large doses of H2O in an already well hydrated body to, say...asparagus and coffee in the first morning pee.