Hook the fuel line to the motor first and then prime the carb by pushing the button until it becomes firm. Then you can start the motor in its normal way. Once started, the motor will start sending air down the second line to the tank to pressurise it. If the tank is nearly empty, you may have to push the button a bit more to keep the motor running long enough to get the pressure in the tank built up. Once pressure has been built and fuel is being pushed to the carb, everything is automatic with no moving parts or diaphragms to worry about.