Plugging return line at tank???

[DDS]

Tank's out again so I'm going to get rid of the the plugged tail of rubber fuel line and properly block the return at the fitting.

Any suggestions as to how? I'd prefer to leave myself the option of plumbing a return in future.

I'd been thinking of making a metal disc, basically a crush washer with no hole and placing it onto the fitting, maybe using some goop of some sort to help seal it. Copper crush washers are often used, could I sand a penny flat and use that, or is it a harder alloy?

Any thoughts? TIA

Dave