Daishain’s 5e D&D Rules, Q&A, And Support The Dedicated says...
The censer's summons only works for an hour, after which the elemental disappears, so it's not good enough for the purpose we need it for. It'll have to be a high-level summons to get a permanent power source, or maybe a quest into the elemental planes to capture an air elemental.
EDIT: Ring of Air Elemental command would be better, but a bit too convenient to find in the horde. Find an Air Elemental, Dominate Monster (With a Bardic Insp and Bless going, maybe?), and force it into the tube within the hour.
Edited: Gknightbc on 3rd Jan, 2018 - 4:47pm