Replacing sending unit- how low does the tank need to be???

I broke my Original sending unit while trying to remove the crusty old fuel line. Replaced it with one from oreillys and it was bad right from the box. I exchanged it and the second one always reads full. I kept my original and plan on brazing the tube back on this spring. I lost nearly all of my fuel when I changed it. So, pump/siphon it down as far as you can get it and hope for the best! It is EASILY replaced without removing the tank. I've removed it with the old 7 1/4 axle and my 8 3/4 in the way. Pulling the tank or axle out is a waste of time if no other repairs are needed.