Z1OwnersClub GB

On the carbs of my 550 project, an american bike, there are two pipes to the tank, one is the flow inlet, the other is a vacuum or pressure pipe for the tank, how exactly does this pipe work, and if I try to start the engine without a tank fitted, does this pipe need to be left open or blocked to help the motor run ? not sure

the second one is a vacuum line to operate the fuel tap to allow fuel to flow to the carbs,if running with a remote supply blank off the vac pipe,I usually push a suitably sized bolt into it