I had a friend in college who did that. This kid also liked to get black out drunk on vodka while on anadrol too. Needless to say the abcess/infection was just the beginning of his doctors meetings when they ran his blood.
They are called single use syringes for a reason..........use them once and throw them away. I know times are tough all over, but the risks of rubber plunger deteriorating and contaminating your gear and making you sick is not worth saving the pennies. Shit I'll eat my food cold before I would save money by doing what you propose!!!