got my spare sending today from a forum member here. it answered a question i have seen many times here and other forums. this concerns whether to use the vent line (5/16) as a return. i have read where some high pressure electric pumps will move a ton of fuel back to the tank. i'm talking about the two line sender (feed and vent). i myself was thinking about using this line for a return with the holley blue or other good pump. i have read where people had to install a bigger return because the 5/16 was too small. if you look at the pic you can see that the vent has what i would call a tremendous restriction right under the top. it looks to me that any fuel going back with this line would smack right onto that blockage and create one hell of a splash and fumes inside the tank. the pencil points to the restriction or whatever you would call it. i plan to modify that line by removing that metal block covering the factory return vent and install the line down to the side and under the fuel level. i now understand why this should be vent only but can be modified. more specific my 81 malibu. maybe if that metal covering was not there you would not need a bigger return. lets hear your thoughts. thanks, Denny