Nowadays we know that we can never disinfect completely a syringe, so that is why we don't do it and we use a new one every time.
Although the best way to disinfect a syringe may be the following method:
Disinfect the syringe using sterile cotton balls soaked in 70% alcohol. Rub all the surface of the syringe with the cotton until you feel that the alcohol covered everything. This will kill most bacteria but not everything.
Sterilize the syringe using an autoclave machine. An autoclave machine is nothing but a special pressure pot that uses steam pressure and heat to kill most of the organisms, except spores and heat-resistant bacteria.
Just to help more the probabilities of killing the most part of microorganisms, repeat the step number one. Use alcohol after taking out the syringe from the autoclave.
Use the syringe right away or it will get infected again in a matter of seconds.
