Fuel Tank Testing

I have a dry fuel tank and new metal fuel line from the tank to the fuel pump. It is a multifuel tank with a bad pump. That doesn't matter because the pump is too much for the Holley carb on the Gasser engine anyway. I want to use this dry tank as a way of figuring out my minimum pick up fuel level. That way I can notch a broom stick or something with the minimum level and keep it in the cab so no matter what the gauge says, I will "know" when I am really empty.

I see several different ways of doing this. Compressed air, vacuum and the mechanical pump on the engine itself.

Compressed air means sticking an air line on the engine end of the fuel line, push air through the line and add measured amounts of fuel until I hear bubbles. Not the safest for the person having to stand by the fill cap and smell fuels forced out while listening for bubbles, but could be the fastest way.

Vacuum is doing the same basic thing with a vacuum pump hooked up where the engine fuel pump would normally be and adding measured fuel until it sucks it to the vacuum pump. Probably the most vehicle friendly and accurate.

There are two ways to do the engine pump method. Pull the spark plugs and turn the engine over on the starter or just use the hand primer arm on the pump with the line to the carb pulled off. This is the more realistic test, but I don't like the idea of running the pump a long time dry. Plus, how many of you have had mechanical pumps on other engines loose their prime and never seem to work?

Another method would be a combination. Use the compressed air to get bubbles, stop. Vacuum fuel to the pump, hook it up, start it up and let it idle until it runs dry.

Any thoughts?

Thanks

You could put exactly X gallons in the tank from an X gallon container, disconnect a fuel line near the tank, separate your fuel line, attach rubber hose, and syphon back into the container- The syphon will stop at just the right time. If the container lends it's self (square or cylindrical, not tapered, you can measure to figure out what you just got back with just simple math, or you could then refill the container which would take the same amount as what was left in the tank.

Or if you ONLY care about the level of the reserve at the bottom of the tank, and not the actual volume, then as soon as the syphon breaks you can stick the tank and you'll have the answer.