Re: Tinsmith's in frame gas tank for cantilever Schwinn.
Those are both good ideas. I'm figuring at some point to dismantle the bike that tank is on (to repaint it) A slot in the filler tube is a good idea. As you say, a worn cut off wheel would work and I also have some dime sized diamond embedded metal cut off wheels I got at Harbor Freight. One of those would work nicely... then flush out the tank well to remove the filings. I would think that a small brass or even copper vent tube would be fine with a lot of care given while soldering it in place. I think I'd opt your cutting a slit approach. Thanks!
Someday when I grow up I will probably lose interest in toys with wheels, but until then...