won't a bolt in the line as a plug keep the gauge
from working? it would trap vacuum in there.
like when you cover a straw with your finger, and
the liquid stays in suspension?
^ It would stop it from working. Similar to a hammer arrester in plumbing, it would trap air in the tube and simply pressurize it as the fuel fought to get to the top. You would have to have an air bleed at the top to allow it to escape. Then it would work.