I realized I needed a fuel return line for my EFII when I receive my engine. I'm glad I realized it before I finished my tanks. I purchased these bungs from flyefii.com for $35 each. One is on each inboard rib.
I used proseal and sealed it flush to the outside of the inboard rib. I made sure it was not interfearing with joining to the fuse!
I also had to make sure the fuel return was at least 3" from the fuel supply. I have it mounted on the opposite side. Being mounted here I will have no issues with any air bubbles being returned and sucked into fuel supply.
