Two people fill their asses with air using a bicycle pump, air compressor, etc. Then proceed to sink themselves in a body of water using large stones until they reach the bottom. From there on the use the air in their asses to keep them oxygenated prolonging the amount of time they have for underwater exploration.
Josh - "Al and Sean have sure been down there for a while"
Savanna - "Yea, they're probably the best Canadian Snorkelers I've ever seen"