1986 VF500F Vacuum tube to fuel tap / petcock (not a California bike)

Ok, got the bike running. I replaced the whole vacuum diaphragm in the fuel tap, got it running and then after a couple of minutes the engine stopped. I had a look at the main line from the fuel tap to the carbs and it is dry, no evidence of fuel passing at all.
There are two other small spigots on the fuel tap. One seems to be used for a vacuum test tool and looking at the manual, it seems I should connect the other one of them to a vacuum line of some sort. However it is not connected. Originally the bike ran ok but that was because the diaphragm was broken and fuel just passed but at the same time it overflowed and I had fuel everywhere.
I assume the vacuum line is to open the diaphragm and let fuel pass when the engine starts.
Does anyone have any idea what I need to do please?

Thanks

Mike

 

The spigot on the diaphragm cover is the vacuum port, the other sticking out the side is a breather port, no line attached to it.

 

Thanks. I also found a really good article here which eventually got round to describing the problem. I appreciate you taking the time to answer me.

Mike

 

Ok, thanks, all running ok. Now on to the next problem, whatever that is