[Jrainman]

You will need to run a vent line ,even if you have a vented cap , the agitation of the fuel from the return line creates more pressure in the tank ,,also remember todays gas is oxgenated , your return line must be at least 3/8 , with the way I set my fitech system up I used the 72 style vent that comes intergrated in the 72 stock sending unit . the vent line I think is about 5/16 anyhow it it seems to be a sufficent size , I never have experienced any pressure build up as of yet in my stock tank with the way I installed my fitech 600