Re: Common Chamber?
This is very simple... A common chamber is when the hose port and the ball barring "blow off valve" share the same area. A non common chamber is a hookah that has individual piping from the hose port and blow off port going into the vase. Kinda like their own stem going down. Common chambers are good for the fact that you can drill more holes to allow more smoke, but they get rusty inside of that are because there is no way for the moisture to completely leave that area.
I hope this helps... if you need I will do a diagram for you.