Sometimes when I vape dmt, after holding the hit at least 20 seconds, I will exhale huge milky clouds of vapor. However, there are times when no smoke/vapor is visible upon exhale. This has been experienced with my glass vapor genie as well as my healthstone pipe. Even when I can see no vapor, I can feel the hit in my lungs and experience the effects of the dmt. Why such a variation from smoalk to smoalk?

I would guess it could have to do with the temperature that the spice vaporized-- and density of the oils as well that come along-- I've noticed similar variations

Possibly your visual acuity or mental perception varies with the effects of your efforts also.

Hummm...

My bet is that although practice makes perfect, in theory, in practice choosing an appropriate design (e.g. with provisions actually promoting reproductability) may help a lot.

Maybe try to explicitly inhale fresh air at the end to make sure all the smoke gets into your lungs where it can be absorbed. See if that makes it more consistent.

Without being explicit about inhaling fresh air, the amount of smoke stuck in between your mouth and lungs will depend on how your hit ended.

My opinion is that completely perfectly vaporized Spice will never give any clouds when exhalting, but doing Changa does it, as you will always burn stuff and therefore create clouds with toxic incineration products just like when using a cigarette.

Therefore the clouds of perfectly smooth vaporized Spice are very thin and not really recognizable, while doing Changa fills a bong with thick white vapor. If you would compress that clouds into a solid brick, this would be a black mess of tar - cant be avoided when doing Changa with a lighter (any sort of).

This made me quit Changa as when I looked at the bong at the end and observed the nasty black residues that I also inhale, I felt bad for my body .