you could not pay me enough money to let the fuel run out on my old TO-35
carb will start sucking all kinds of bad stuff out of tank to keep running.
keep or add a inline fuel filter to your fuel filter system and change it every year.
even with your best efforts, we get dirt and rust out of old fuel transfer tanks/cans, funnels, etc:
I just would not want to run the tractor out of fuel, if I did not have too.