I learned only 5.6% of oxygen is absorbed in each breath. And that gave an idea.

The percentage for THC is probably relatively small too.
Which means that the smoke/vapor you exhale still has 94.4% of THC after you hit.

Introducing:
Take a balloon, take your hit
blow the smoke/vapor into the air
let the balloon push the smoke/vapor back into you.
Repeat to observed effect.