When bottom painting you want to make sure the paint is well mixed. The solids often settle to the bottom of the can by the time you bring it home from the store. So the night before, store the can upside down to start releasing some of them into the solution. Next, get yourself a drill motor and a paint mixer like this one. Now you see, when you put that in the can there may be some splash. But here's the tip: take a scrap of cardboard, poke a hole in the middle and you can mix to your heart's content without splattering paint all over your nice power tool.