A brass clunk?? why not use an aluminium inline fuel filter that has a brass nut screwed onto it, clunk and filter in one
and while your at it, why not use tubular heat shrink over the entire tank. Get a piece thats almost the same diameter as the tank and a little longer. When you hit it with the heat gun (carefully) the excess ends will shrink and make the thing try to go a sausage shape as the unsupported ends shrink and pull the top tighter on.
what anyone think of that?