Well, James… A 'Dryer' is not just to dry the gas on its way to the air intake system, but it has another VITAL function!
First you need to have absolutely clean gas (with NO NaOH or KOH) entering the intake system. They are highly corrosive materials. Next, you need to have the gas DRY, so as to prevent any chemicals from entering your engine.
BUT Second… the most important thing is to help prevent a FLASHBACK from your engine, traveling through the tubing and exploding your reservoir and possibly your HHO generator!
You see, HHO gas is 2 parts HYDROGEN and 1 part OXYGEN! Oxygen is the KEY to allowing the gas to fuel itself. Hydrogen by itself, will not burn, but oxygen, it is a perfect combustion mixture!! That's is why it is such a good catalyst for your fuel combustion.