Depending upon the flow rate, the carbon dioxide should be admitted into the chamber for at least 45-60 seconds. The animal is then placed inside the chamber and the lid secured. Additional carbon dioxide gassing for approximately one minute will usually be sufficient to complete the process. Before administering gas, the ground glass surfaces should be sealed with silicone grease. Various commercially-available or customized tops allow a glass aquarium to serve as a euthanasia chamber.
Similar tops are available to euthanize animals inside plastic rodent cages .
The simplest functional system is one that has a single hole through which a length of tubing connected to the regulator passes. The tubing extends down to the very bottom of the chamber and does not quite entirely block the hole in the lid. This system allows gas to enter at the bottom of the chamber while air is vented out through the small opening around the tubing at the top. A small hole is punched in the lid to serve as an inlet port, through which can be passed a length of plastic tubing attached to the regulator from a carbon dioxide cylinder. Use of a durable transparent plastic for the lid will assure that the animals are visible and can be observed during euthanasia.