there are two tanks.  on tank has a fill line and a line to the pump.  the vent line is connected to tank #2 pickup line.  the 2nd tank has a vent, that is it.  when i fill tank #1, once it fills all the way with fuel, the fuel then overflows into its "vent line" which then fills tank number 2 thru the clunk pickup line.  i had a great smoke trail.  i also decreased the pumps speed to about 1/3 speed, even then, there was still some oil on the wings, i may have to further decrease the rate.