To OP:
I've never used a GVG or a regular Vapor Genie, but a definite way to smoke high doses of DMT in one hit is by making enhanced leaf.
I never use any MAOI's in my enhanced leaf blends.
I mix them at a ratio of 1:1, DMT to peppermint leaf.
I shared some of this DMT-enhanced leaf blend with a friend, and because he liked it so much at lower dosages, he ended up doing way too much on one particular occasion.
I would estimate that he put about 200 milligrams of the enhanced-leaf smoking mixture into a bong with a large bowl piece, and smoked it all in two large inhalations.
That would be the equivalent of vaporizing 100 milligrams of pure DMT.
He ran to the bathroom and immediately vomited in the sink, his face exploded into fractals and a bunch of small lizards which scurried away quickly, the sink and bathroom were no longer there, and was replaced by an ever-expanding universe, infinitely stretching out in all directions.
He told me he perceived eight layers of reality simultaneously, and kept puking although there was nothing left in his stomach, and was ridding his diseased soul of sickness and evil that he had been harboring for a very long time.
I obviously do not recommend smoking this much at once, but my point is that when using DMT-enhanced leaf blends, especially if you make them yourself and at a ratio of 1:1 leaf material to DMT, then it is quite easy to ingest large amounts of DMT quite easily and consistently.
I think that this approach works better than any type of vaporizer pipe one might be able to purchase.