HELP gpx 250 fuel issue

Hey guys, could be the amount of beers I have had tonight, but I thought fuel came out of the tank to the carbs?
Im working on a chugging problem my girlfriends gpx 250 has developed. Noticed no fuel was getting to the inline fuel filter bellow the fuel tap. I took the tap part off the tank, I can blow into the pipe with a bit of force and get air through, but i cant suck air from the tank side to the tap side.
Am I doing something wrong here?
Am I not seeing something?
Am I too drunk?
What purpose does the diaphragm serve inside the tap?
I thought when the tap was on, fuel flowed freely from the tank?
Im working on a chugging problem my girlfriends gpx 250 has developed. Noticed no fuel was getting to the inline fuel filter bellow the fuel tap. I took the tap part off the tank, I can blow into the pipe with a bit of force and get air through, but i cant suck air from the tank side to the tap side.
Am I doing something wrong here?
Am I not seeing something?
Am I too drunk?
What purpose does the diaphragm serve inside the tap?
I thought when the tap was on, fuel flowed freely from the tank?