Been searching.
Found a post that said the line I thought might be a vacuum line, IS the fuel out line. I sorta thought so at first but I pulled it apart and no fuel came rushing out. Nothing came out. So either the tank is empty (but showing over a quater) or the screen is completely blocked, or thats not the fuel line.
So which is it
here is thw two pics with the blog. Blog is about replacing tank strainer in an 87SD
Blog says the pic with one fuel lines is fuel out with strainer above it in the tank
Other photo of Two lines going into the tank it says is return and Vent. But on mine the two line side (passenger side) has both lines plumbed. Unfortunately Im just little to big to crawl under the car and follow the lines.
here is the whole blog address
http://biodieselbob.blogspot.com/2008_07_01_archive.html
pics are about half way down the page.