The pump arrived today, and after fixing it to the battery pack and hooking up the air hose I switched everything on, and placed a finger over the air return. It works. Air flows readily through the entire system and based on tests conducted yesterday, the habitat is fully watertight. It's done. Everything is in place. All that remains is to spend the day testing it above water, in the bathtub and in the pool. Tomorrow, we launch.
UPDATE: over-water tests concluded, hamster seems fine. Started bathub test about 15 minutes ago:
The sound of rushing water sent him into a panic, but once the faucet was turned off and the tub full, he settled down pretty fast. There he is next to the light. I just checked on him, he's eating, looks pretty mellow. Doublechecked pump, air's circulating, so far so good.
UPDATE: Removed habitat after one hour. Resounding success. No ill effect, he didn't eat, drink or poop much and the battery pack hasn't depleted by even one bar. This bodes well for the possibility of longer term deployments.
UPDATE: Here's video from the interior during the bathtub test.