When you pull back the plunger and let air in the syringe to get air bubbles to the top or what not. How do you know there is no bacteria or dust in the air you're letting in? I have a clean house but i don't know if my air is clean. Also, how do you know if you have an abcess? An abcess is pus build up right? Also is it possible to get an absess by injecting something with tons of BA in it?