The outlet line you saw went into the hole on top of powerhead outlet to get more water flow over bubble through diffuser...( not all powerheads have this feature )
it actually increased efficiency by constantly pulling water past CO2 pocket. You may think diffuser is not working until you lose your CO2 supply.
When my yeast mix slowed on production and couldnt keep up with replenishing the CO2 pocket it would completely diffuse the pocket in about 4-5 hours. (thats a lot of CO2 )
That told me that it was really doing its job because that bubble never escapes to surface so it has to be going somewhere... hehe