My own findings are not entirely consistent with some things mentioned here.
Nice toys you have there!
Just read this thread, my 2 cts...
I use very small test tubes and suck hard as it evaporates. Some of it always condenses on the walls. If I don't inhale fast enough, some will escape at the open top.
I simply stick a thin glass tube into the test tube and keep it a few centimeters above the dmt. Ideally, the thin tube is bent 45 degrees such that the end is a few cm above the bottom of the test tube. Very efficient but requires some practice.
I find underheating more often a problem than overheating. The glass is supposed to protect the spice from the open flame and I think it does that well. The risk of actually burning your dmt is much higher in open-flame methods even despite protective layers of ashes etc... at least in my experience.
I wonder if what's called 'burning the dmt' actually is pyrolysis of residues and/or scorching of DMT vapor by the hot glass - not literally burning, in the sense of reacting exothermally with oxygen. Try to burn a bit of naphta, xylene, candle wax or other flammable stuff in a testtube!
A boiling pure liquid substance doesn't rise in temperature: adding heat results in more vigorous boiling. At least, that's the theory... we all know something like 'burned dmt' exists and is not nice