1984 c20 fuel filler neck connector

[82k10ny]

hey guys first post here and this seems like a good spot to ask this on my 84 c20 camper special with dual 20 gal tanks it has a hard pipe that connects both filler necks so you can fill either tank from either side. it looks to me to be aftermarket and i dont know of it being a factory option. the issue i have with it is that where the crossover ties in is right at the turn in the filler neck to go forward to the tank so when filling its more of a straight shot to the opposite side tank. say if im filling into the drivers tank gonna put 20 gallons in it puts 15 in the passenger side and 5 in the drivers side give or take and vice versa. has anybody had a truck with this setup before and know more about it than I? im thinking that maybe once one tank is full its designed to overflow into the next one. which is all fine and dandy if you have 160 plus dollars for 40 gallons of sunoco 93. i had it one time last summer it brimmed the pass side tank so full that sitting in the sun at work it started spraying fuel out the vent on the tank from expansion.

any product info, links or anything would be greatly appricated.

thanks