So this was what my 20 year old mind could come up with in the "McGyver department" Yes it was 25 years ago; but still, it gets points for originality.

We wanted to smoke pot underwater.

I used an U/W camera case with a second stage attached to the front.
The lp hose went to the 1st stage on the tank.
A mouthpiece was attached to a hole in the the back of the housing.
This was kept plugged until ready for use.

A hole was cut into the bottom of the case and a neoprene glove finger (waterproof, right?) was inserted and glued into the housing.
Your smoke of choice was inserted into a roach clip, (roach clip; remember college?)and a bic lighter, that were glued strategically next to the glove finger.

Once underwater, you put your finger in the glove, flicked the bic, and pushed the button on the second stage, and inhaled.

Woo Hoo!

(Beers with twist off caps were actually much easier.)

Remember kids, don't try this at home!!!

I haven't thought of this for years! Sorta like a flashback!
(Flashback = buy one; get one free!)
I think we were the Dive Pirates of our day.
ASW