I know the pain you are in.
I just got a 81-82 points c70 and my tank is all rusted out.
http://www.mopedarmy.com/forums/read.php?18,2941417
Got to reline it, which will cost as much as buying a tank I'm sure.
I think the design is dumb. NO petcock, and 2 outlets.
shesh
who puts a cock on a carburetor.