Some Moeller tanks have a pick up that rotates and locks in position. If that’s the case with yours, I was told by Moeller that you can’t unscrew the pickup. I did discover that if you pull-up on the fitting, the tube along with the o rings that seal it pulls right out. I don’t know if it damages the fitting or not, but if it does, at least you know you can get a PE tank which will cost less than custom alum.