[Brian]

Set the fluid level on the empty mark in the gauge. Hook up the air line and drive the car. The fluid should automatically rise and record the tank level after a few miles of driving. The fuel sloshing around in the tank will create pressure within the airline which causes the level in gauge to rise accordingly. If you blow the fuel line back to the tank, you're artificially creating pressure in the airline, so obviously, the liquid will keep on rising. Don't blow through the fuel line back into tank!