take an acrylic tube or even a large (but clear) plastic see through bottle of any sort. Cut it in half. Put a humidistat inside, and plumb a nipple to be able to attacth your HHO line in. Reconstruct it so it is sealed again to a great degree anyway, with tape. Sit it with one end open on a seat of dessicant until the relatively humidity reaches about 10%. Slide it off the dessicant and open up your HHO flow. the HHO will displace the air and push the other air out the small crack that are left. Let it run 5 or ten minutes to flood the area. Wait. If the humidistat goes way up - you got water. Plausible?