Abstract: The present disclosure includes a method comprising positioning a nose of a rodent within a nose chamber of a device for anesthetizing the rodent, the nose chamber configured to partially enclose an anesthetizing gas and hold the nose of the rodent in contact with the anesthetizing gas, delivering a positive flow of the anesthetizing gas into the nose chamber through a gas intake channel sufficient to anesthetize the rodent, supplying a waste gas reservoir to collect the anesthetizing gas, the waste gas reservoir in communication with the nose chamber through a gas transport channel and coupled with the nose chamber in an open configuration allowing the anesthetizing gas and ambient air to flow into the waste gas reservoir, and actively retrieving the anesthetizing gas and ambient air from the waste gas reservoir with a negative flow conveyed through a gas outtake channel in communication with the waste gas reservoir.