RE: 1/2a fuel tanks
Visine bottles are nice, they hold 14-15cc and are made from LDPE like flex tanks, so they seal easily. Adding a fuel line to the spout is chled's play, then you are left with fitting a vent. I have had the best luck cutting self-sealing holes using slightly undersize Al tubing, sharpened a bit and heated just hot enough to barely cut through in one pass. If your hands shake the hole gets bigger.
My balloon tank rig uses the neck of a Visine bottle as the closure fitting. I think it works real slick.
MJD