It's a process of separating the acetaminophen from tablets like Percocet, vicoden and codeine. They call it a Cold Water Extraction. It's recommended if a person wants to take more than a few pills to do this because too much acetaminophen can be toxic. I'll find you a link.
There are a lot of methods. I like to shake mine, not stir. Also I take a straw and just drink down the cold water on top, getting all the good stuff while the garbage APAP is on the bottom of my clear glass bowl , and then it makes extracting that little bit at the very end much easier than straining the entire batch with a coffee filter or wet paper towel OR whatever you use.