This plastic Syringe will do the same job of a priming pump plastic pump for a fraction of the cost.
The purpose of a priming pump is to help prime your home machine in case of an air lock (this can happen with brand new machines as well as in-use machines if air enters the system or they sit unused for few days).
Before using this syringe, make sure that the steam/hot water outlet knob is open and the pump is working. If the knob is not open, back pressure will prevent water from entering the pump.