It unscrews just like a mason jar, problem is it is just damn tight. I tried using a big ass screwdriver to lever on off the other day, too lazy to go get the correct tool and there was no moving the darn thing. I finally got the special tool out of the cabinet and even then it was a bit of a buger to do. Back in the day before we had the monster hose clamp around them they were much easier to do and nobody used the tool but now when you come up against one they have been on there for years and years and have that big hose clamp squeezing it all together so that even after you take the clamp off they are just a bear to undo. A big part of the problem with trying to lever them up and off with the big screwdriver is that it distorts the shape of the ring and causes it to bind. Maybe if you could get one pushing up on the right and one pushing down on the left it would help to maintain the circular shape of the ring and facilitate getting it off.

Just to add, you haven't even got to the fun part yet, wait 'til you try to reinstall that darn pump/sender assembly. You might find it easier to deal with if you remove the spare tire assembly and crawl clear into the trunk to work on that POS, depends upon how big or small you are. I am 6'1", 260 and still find it easier to crawl all the way in with the spare removed instead of leaning all the way over that crap and standing on the ground.

Mark