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Expand-a-Lung on the cheap! Dive further, deeper, longer on one breath.

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Step 2: The valve

Picture of The valve
The valve is a device that appropriates a restrictive element to a chaotic force (try not to picture a parent leashing their child to their wrist in the Jacksonville (or nearly any other) airport via Monkey-tail leash. Instead, think: dam).

In our case, the valve should be plastic. The lighter the better. And make sure one end is relatively circular.  I browsed the hardware store for nearly 2 hours fitting all types of valves to the pictured mouthpiece and finally settled on the hose adapter. Its light, sturdy and cheap: about 3 bucks.