I know that after drawing up oil you should change the needle before you inject into yourself. But should you change your needle between drawing from more than one vial of AS? Say that I am going to shoot 1cc deca and 1cc fina with one syringe, should you use the same needle to draw from both vials, or should you change needles before drawing from another vial to prevent some deca getting into your fina and fina into your deca?