I ran into the same issue after adding my new 3/8" sending unit and then buying a 426/440 vapor separator off of YO.
I fixed it buy going to my local NAPA and buying their Gold #3054 filter/separator. It is an in-line fuel filter with a return line off of the side of it for $6. Then just clamp on your return line.
http://www.napaonline.com/MasterPages/NO...l+Filter+(Gold)