Originally Posted by coypoo
[...]If I take an early sample from the keg, is the beer in the line at the same carb level as in the keg?
I just reread this, and it's a completely different question than the title and the first question.
If you hook up a keg and draw a sample, it will be more or less representative of the carbonation level - at least near the end of the Out dip tube. Caveats include explosive overcarbonation that causes a cascade effect knocking most of the carbonation out of solution...etc.
Otoh, if you hooked up a flat keg to, say, a picnic tap, drew enough to fill the tap line, and then started the carbonation process, I expect it would be a long, long
time before any sign of carbonation made it the length of the tap line...