Good luck in seperating them. My experience is that more often than not it is best to remove the pan with the filler tube in place and remove the brace on the bellhousing bolt to enable taking them off together.

I have seen that others have actually cut the tube and then used a piece of hose to bridge the cut through section and secure it with clamps upon replacement of the pan.

However, if you want to give it your best effort the outer (larger) hex shape is actually part of the pan while the smaller is what turns to remove the filler tube from the pan. Good luck.

Randy