I got a 1976/77 b200 camper van , 360 . I got a new tank says it's the right one but was different than original I got the new sending unit for it . Got it hooked up and tried starting , no fuel . The sending unit won't pass gas , I took line off and tried sucking nothing but fumes , I blew in it and hear no bubbles it just pressures up and blows air back out , what am I missing I can't figure it out .

 

Wrong port. That's either a vent, or return line.

Do you have a pump in the tank? (I am guessing probably not.....)

 

Van of that vintage has mechanical fuel pump.
They had either a 20 gal or 36 gal fuel tank.
Mine is a 36 gal plastic tank, the fuel sending unit sits in the top center.
there are three ports coming out of top of the unit. one is for fuel evap system, one is a vent going back to top of fuel filler tube and third runs to the fuel pump.
If I remember correctly looking from back to front the line running to fuel fill tube is on the right, to fuel pump is center and the fuel evap is left.
to confirm, if your tank is out look at the fuel sending/float unit and you should be able to trace the line from the pickup screen to the top of unit.