Kerosene/petroleum based fuel of your choice (Kerosene is the least likely to explode and/ or make you high) with good (go outside) ventilation. Citrus degreaser also works reasonably well if you add a bit of water to it, is friendly on plastic, and doesn't have the same fumes. However, if it says to add water, do. If you don't add enough water in my experience it actually doesn't work as well.