don't forget fleet/farm supply stores have LOTS of vacuum hose for 
milking systems.  it's usually clear but very thick wall to stand up 
to close to 30" vacuum.  substantially cheaper than auto sources.

please don't use heater hose.  i shudder to think i'm meeting people 
on the road with soft, collapsable heater hose supplying vacuum to 
their brake systems.  as i've said before, "don't f*ck around with 
brakes."  end of sermon.

-dan