No SWIMing and no dogs allowed, except for actual meth-bonging, essential-oil huffing ones, which, though you may scoff, do exist; one of them behind me right now. All the shards on my fingers and floor and desk and bathroom and kitchen, it's no wonder the cat is jumping at random spots on the wall at 3:30am and my dog seems to be talking to her self.
Then again, I'm pretty high too, so it might be just me. Anyway, adding oils seems really weird to me. I still can't get the stale-toothpaste minty taste out of my mouth after using old nicotine gum to seal the holes in the plastic peanut cannister I used for my DIY mark 1 meth bong.
BUT, the meth molecule isn't very reactive by itself, it's fairly inert and stable. Essential oils are, y'know, oils. Meth-HCl, being charged, would stay with the water phase and never interact with the water-fearing oils.
BUT BUT, sorry "dog", you bring up a great and, in fact, timely mystery around vaping meth. An open question that a real chemist could answer real fast: what is the protonation state of the meth when it leaves your bowl? Sure, it's the acid salt you put in your bowl, not the base. But there's some issues with vaping a salt, and the possibility of meth base actually vaporizing along with tooth-rotting HCl gas. These would possibly recombine on the way down the pipe and into your lungs.
This makes the feasibility and yields of drawing the vapor through water questionable. If the meth is the protonated, acid form, it's water soluble. You're leaving all your drugs behind in the bong water. If it's in fact predominately in the base form, it would not dissolve in the water. At a different time months ago while high, I proposed an experiment wherein the pH change of the water after a long session could be used to answer this question. And a multimeter could be used as a pH meter.
Well, I tried to DIY the vapor in my bong to actually pass through water, but there were multiple issues with my designs, and I barely escaped with only one reflux explosion.
So I don't know if it would interact with the water or the oils. But, even if it was in the oil phase, I doubt either inert compound will react. Personally, I wouldn't want to huff that much essential oil. Keep in mind this is 400F gas hitting it, too. There are anecdotes of kids and pets getting sick from concentrated tea tree oil. I'd stick to one toxic vapor at a time, mainly the one that gets you high.
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EDIT: to those who say, why are you bonging if your bong has no (actually a tiny bit) water? How is it a bong? Well, it's just a chamber so that 200C jet of vapor doesn't keep searing a hole in my tongue. I have a broken pipe bowl with a bend going into a mason jar, with a plastic straw to draw from. Tiny puddle of water on the bottom, keeps things moist and lets me get the full lung-full massive draws and subsequent fog banks I deserve. Yes I'm proud of my new arts&crafts baby.
Also, as stated, the question of how much you'd leave behind in the water is an open question (for me). In a weed bong, it's actually filtering particulates; the oily THC goes right through. Not necessarily the case with meth, which (should) have no particulates to filter.