I had a problem with a replacement unit. I took it out removed the sock, It too was sucking to the end of the tube. I held the unit and measured from the mounting surface to the bottom of the reach down of the tube. Bent it to approximate the same depth I needed to reach the bottom of the tank .
I went to deep so it wouldn't sit flush in the ring of the tank hole. I bent it up a tad until it would sit flush. Once I got it to fit I cut the end at a V so noting could ever suck onto it.
Now that was corrected I focused on the sender. While out of the tank I ground it with a long wire and attach another long wire from the sending unit plug. Hold it while sitting in the car. Make sure the float is at the bottom of the pick up tube, You may need to bend the wire down.
At this position with the key on, The tank should read empty. As you move it up you will see where the gauge travels to at different heights. Worked for me in several builds. They never seem to be correct when you get them. But with some persuasion you can fix them. I had one I got on ebay from chink land where I needed to add a resister. Never went to empty on a gauge. Always had current flow.
Oh and I never had one out of the box I bought that reached the bottom of the tank to this day. All needed to be bent down . Some more then others.