Reservoir bags attach to both rebreathing and non-rebreathing circuits. In rebreathing circuits they generally attach to the bag hanger on the CO2 absorber. In non-rebreathing circuits they attach to the distal end of the downtube. The downtube also acts as a reservoir, and in cases involving very small animals with minute volumes less than the internal capacity of the downtube, reservoir bags may not be necessary.
