If you mix lets say Ethanol with Petroleum ether and sake it up real good and let it sit for a while your should get 2 layers right? after 2 defined layers are formed and you separate one layer lets say the Ethanol layer then how can you be sure there is no Petroleum ether residue in your Ethanol? And if there is how do you get it out?

There will be a very small ammount as they are very very slightly miscible.
Im no chemist but I imagine using temperature via distillation and evaporation may be a way to separate them..

Why?