http://www2.towerhobbies.com/cgi-bin....pgm?C=GMJ&P=7

I always used the Bru Lines, personally.
Some of the car engine filters will also adapt nicely.

As for the giant stuff, you may have to get a bit
more inventive, if the manufacturer doesn't offer an option.

It's not hard, really... especially if you add a tube
to get rid of the gas spit that some of the carbs produce.
Just find a piece of rubber fuel line that fits over
the tube, and glue/ziptie/etc... a piece of pantyhose over it ;-)