No kidding! I'm so glad I don't have any rust like that.

 

Removing my bed is not the best option, I have a 120 gallon aux fuel tank and drw so it is a pita to do.

 

lol That was from before I replaced the rear tank!

Now its got a nice new tank covered in bedliner and rust everywhere else! LOL

Well then I would drop the tank. Siphon as much diesel out first as possible.

 

Getting a siphon hose down that filler neck / inner hose may be a PITA. Esp. with the extra length/bends of a dually. You have to remove the neck/hose anyway, so you might want to remove it first, then you can shove the siphon down the outer hose. Might even want to pull that outer hose so you can put the siphon right into the tank.