bad fuel delivery 77 c20 dual tanks

[doobiebro]

Hello fellas I have another dreaded dual tanks/fuel tank selector valve question? Here's the story. I have a 77 C-20 that belonged to my father in law. From one day to the next the truck had no power/popping carburetor. After throwing lots of money and parts at it with no luck I realized I over looked the fuel pressure and low volume in the filter. I crawled under the truck and noticed the D/S fuel tank was by passed and the Passenger side tank was only hooked up. That explains why he would only fuel up on the passenger side. The fuel selector valve missing. I have read up on (hatzie) threads. I will need to replace the fuel sender and I noticed both tanks have the same 2 ports fuel sender. One port for fuel delivery and the other is just an open plastic nipple piece. Is this suppose to be a vent based on my pics? I don't believe this truck was designed to have return lines. I will replace all the rubber fuel lines while the bed is move back and get the truck running. Later down the road I hope to get the correct selector valve and get the fuel tanks operational. Any help is greatly appreciated. Thanx.