Electric pump before or after mechanical

I am sure it is evaporating. After investigating, I noticed the pressure gauge shows nada. Pull the Carb top and the bowls are empty. Crank, crank, crank (5-10 secs) pressure comes up, 10 seconds later it fires.
I have checked backflow and cant find any. I believe when I shut down, the fuel in Carb evaporates, needle/seat opens, pressure bleeds into bowls and then evaps some more.
Not sure this is what’s happening, just what I have concluded from inspection/investigation.
I don’t really want to run an electric but not sure what to do about the issue.
Not going to buy a new tank for a return line. Mine already has the charcoal can return capped that I could use but what would that help? Won’t stop the pressure loss will it?