On 28 Mar 2007 05:35:38 -0700, wrote:

My decision now is simply to scrap the idea as stupid, or seek out a
slightly larger bottle (perhasp 2L+) and try again!

Do the maths.

If you really have to, do it by experiment. Fill your compressor tank
and switch off. Then use that until it's empty. Divide that by the
capacity of that tank over the capacity of your portable tank.

There's a _reason_ why SCBA kit needs to run at a squillion psi.