Removing Fuel Sending Unit from fuel tank

[Kenneth]

So I've removed my gas tank on a '76 elky and to find out the rust situation inside you've got to remove the sending unit, which is basically one of those circle things, sitting on top of the tank with hoses coming out, and seemingly have no way to be opened. everybody I talk to says they've never heard of a tool (plumber's tool?) to open them. It seems the tool of choice is a brass drift and a mallet/hammer. I know it may work, but it just doesn't seem right. Plus I'm a bit worried b/c there is a whole lot of rust and I don't want to destroy it while trying to open it. anybody have a better idea?