A device made from one or more gas mask canisters in which to exhale when smoking weed. The military grade canister filters trap any and all smoke and odors.
A perfected iteration of the "paper towel tube and dryer sheets" model, and an absolute must for any DL stoner.
Kevin: "Man, how come Josh's apartment never smells like weed? He smokes ALL THE TIME."
Jake: " 'cause he always uses his hide-a-hit, bro. He invented it, after all."