I'm completely new to the world of DIY, and recently completed my first minor woodworking project. After staining my piece, I cleaned my brush with mineral spirits. Now, every source that I can Google tells me that I can reuse the dirty spirits by letting them sit until the stain settles, then pour off the clean spirits from the top. However, the exact opposite is happening; the stain is separating and floating to the top! What do I need to do in this situation?